Double row bearing device

ABSTRACT

A bearing device comprising a shaft, a housing, a double row of bearings provided between the shaft and the housing and preloaded by a fixed-position preloading method, the double row of bearings having a pair of races with a gap therebetween for preload adjustment, and the bearing device further having a support member for supporting one side of the races in the pre-loading direction, and the support member provided on the side of one of the shaft and the housing.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a bearing device having a double-rowbearing, and particularly to a small bearing device that is used in thespindle motor, swing arm, IC cooling fan motor or the like for aninformation storage device such as a hard-disk drive, floppy-disk drive,or optical-disk drive.

[0003] 2. Description of the Related Art

[0004] Conventionally, two ball bearings, that are spaced by a spacer,have been used as the bearing device for a hard-disk drive. Moreover, inJapanese Patent Publication No. Toku kai hei 10-227310, a bearing devicewith the object of reducing the outer diameter of the bearing whilemaintaining sufficient strength and shaft rigidity has been proposed.This publication is incorporated in this specification by reference.

[0005] In this kind of bearing device, the shaft is formed with twosections; a large diameter section and a small diameter section, and byforming an inner-ring raceway in the outer peripheral surface of thelarge diameter shaft section, the shaft is also used as one inner ring.In addition, the other inner ring is attached to the small-diametershaft section.

[0006] Recently, as the motor of hard-disk drives has become smaller, itis necessary that the width of the bearing (dimension in the axialdirection) be made smaller, for example, 2 mm or less. It has beenthought that as a method for greatly reducing the width of the bearing,a single-row bearing could be used, however, when using a single-rowbearing, vibration or run-out of the rotating shaft increases and it isnot desirable.

[0007] A bearing unit that is capable of reducing the width of thebearing while at the same time suppressing vibration or run-out of therotating shaft has been disclosed in Japanese Patent Publication No.Toku Kai Hei 6-222733, for example. This publication is incorporated inthis specification by reference.

[0008] This bearing comprises two rows of balls, an inner ring, middlering and outer ring, where the inner peripheral surface of the middlering is the outer ring of one row of balls, and the outer peripheralsurface of the middle ring becomes the inner ring of the other row ofballs. In other words, the diameter of the pitch circle of the ballsprovided between the middle ring and the outer ring is larger than thediameter of the pitch circle of the balls provided between the innerring and the middle ring. Moreover, the distance in the axial directionof the two rows of balls, specifically the distance between the centersof the balls is about the diameter of the balls.

[0009] Also, in the case where the double-row ball bearing is setbetween the shaft and the housing such that it is pre-loaded by afixed-position pre-loading method, this pre-loading is performed bylocating the two inner rings with the gap for adjusting the pre-load,and by pressing the sides of the two outer rings such that they areelastically deformed.

[0010] However, in the bearing of the aforementioned disclosure, themethod of reducing the width of the bearing should be improved. Inaddition, in the bearing of the aforementioned disclosure, in order toapply a pre-load to the bearing, a complicated procedure is requiredwhen placing the bearing between the shaft and housing.

[0011] In a bearing with a small width (dimension in the axialdirection) of 2 mm or less, for example, when two inner rings and outerrings with the same width are formed as in the prior double-row bearing,and the bearing is formed with a constant width in the radial direction,the bond margin is not sufficient, and there is the possibility thatsufficient bond strength between the shaft and the housing cannot beobtained.

[0012] The double-row bearing is set between the shaft and the housingsuch that it is pre-loaded by a fixed-position pre-loading method,however, when it is not possible to obtain sufficiently strong bondstrength, as described above, there is the possibility that the positionof the two inner rings (races located with a gap for adjusting thepre-load) will not be fixed, and thus cause the space for adjusting thepre-load, as well as the pre-load, to change.

[0013] For example, the HDD used for a computer memory device comprisesa housing fixed to a frame etc. and a support shaft fixed to thehousing, and a bearing device for rotatably supporting a hub or innermember.

[0014] A single annular hard disc (or discs) has an inner peripheralportion supported by the hub or inner member to rotate together with thehub or inner member.

[0015] Since the hard disc has a thin track for recording data, the hubor inner member must be rotatably supported by the support shaftpreventing vibration or NRRO (non-repetitive run out). Therefore,conventionally, as the bearing device provided e.g. between the outerperipheral surface of the support shaft and the inner peripheral surfaceof the hub, the structure where a pair of ball bearings are combinedwith each other, such that a preload is applied to the balls in thebearings so as to sufficiently secure the bearing rigidity.

[0016] JP Patent Publication Toku Kai Hei 10-159843 discloses such abearing device. This publication is incorporated in this specificationby reference.

[0017] In this structure, the support shaft has a base portion fixed tothe center portion of the housing, and the bearing device has a pair ofball bearings are provided between the tip end and intermediate portionof the support shaft and the radially inner cylindrical portion withinthe hub. The inner races of the bearings are fixed through interferencefit or adhesion to the tip end and intermediate portion of the shaft.The outer races are formed with cylindrical projections provided at anaxial end and axially projecting than the end surfaces of the innerraces. The tip ends of the projections are abutted to each other, andonly the abutment portions of the outer races are fitted into theradially inner cylindrical portion of the hub. There are landscircumferentially provided on the radially inner side of the axiallyintermediate portion of the radially inner cylindrical portion.

[0018] In this bearing device, a desired preload is applied to the ballsby pushing the inner races to come closer to each other with a gapprovided between the axial end surfaces thereof. And, the hub isrotatably supported around the support shaft with no play under thepreload.

[0019] Incidentally, when the bearing device under preload isincorporated in a narrow space, generally the bearing device ispreloaded through the fixed position preloading method. There are twoways for mounting the bearing device preloaded through the fixedposition preloading method to the support shaft.

[0020] 1. a pair of inner races are fitted onto and fixed to the supportshaft through interference fit applying a load to have the inner racescome closer to each other.

[0021] 2. a pair of inner races are fitted onto the support shaftthrough clearance fit, and bonded for fixing under a load to have theinner races to come closer to each other.

[0022] The installation of the bearing device to the shaft in either wayabove can be carried out only by the bearing manufacturer who has aspecial apparatus to highly precisely apply a desired preload to thebearing device.

SUMMARY OF THE INVENTION

[0023] Taking the problems with the prior art into consideration, theobject of this invention is to provide a double-row bearing that is setbetween the shaft and the housing such that it is pre-loaded by afixed-position pre-loading method, and that will make it possible togreatly reduce the width of the bearing to 2 mm or less while at thesame time suppress vibration of the rotating shaft, as well as reducethe number of components and make it possible to perform pre-loadingmore easily when setting the bearing between the shaft and the housing.

[0024] Moreover, another object of the invention is to provide a bearingdevice having a shaft, a housing and a double-row bearing that is setbetween the shaft and housing such that it is pre-loaded by afixed-position pre-loading method, and that prevents movement of the tworaces, that are located with the gap for adjusting the pre-load, suchthat no change occurs in the gap for adjusting the pre-load, even whenthe width (dimension in the axial direction) of the double-row bearingis extremely small or less than 2 mm.

[0025] Another object of the present invention is to provide a smalllightweight bearing device having sufficient rigidity under preload,through reduced manufacturing steps for cost reduction, and for a longdurability of performance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a cross sectional view of part of a bearing deviceaccording to a first example of the embodiment of the present invention.

[0027]FIG. 2 is a cross sectional view of part of a bearing deviceaccording to a second example of the embodiment of the presentinvention.

[0028]FIG. 3 is a cross sectional view of part of a bearing deviceaccording to a third example of the embodiment of the present invention.

[0029]FIG. 4 is a cross sectional view of part of a bearing deviceaccording to a fourth example of the embodiment of the presentinvention.

[0030]FIG. 5 is a cross sectional view of part of a bearing deviceaccording to a fifth example of the embodiment of the present invention.

[0031]FIG. 6 is a cross sectional view of part of a bearing deviceaccording to a sixth example of the embodiment of the present invention.

[0032]FIG. 7 is a cross sectional view of part of a bearing deviceaccording to a seventh example of the embodiment of the presentinvention.

[0033]FIG. 8 is a cross sectional view of part of a bearing deviceaccording to a eighth example of the embodiment of the presentinvention.

[0034]FIG. 9 is a cross sectional view of part of a bearing deviceaccording to a ninth example of the embodiment of the present invention.

[0035]FIG. 10 is a cross sectional view of part of a bearing deviceaccording to a tenth example of the embodiment of the present invention.

[0036]FIG. 11 is a cross sectional view of part of a bearing deviceaccording to a eleventh example of the embodiment of the presentinvention.

[0037]FIG. 12 is a cross sectional view of part of a bearing deviceaccording to a twelfth example of the embodiment of the presentinvention.

[0038]FIG. 13 is a cross sectional view of part of a bearing deviceaccording to a thirteenth example of the embodiment of the presentinvention.

[0039]FIG. 14 is a cross sectional view of part of a bearing deviceaccording to a comparative example of the embodiment of the presentinvention.

[0040]FIG. 15 is a cross sectional view of part of a bearing deviceaccording to a fourteenth example of the embodiment of the presentinvention.

[0041]FIG. 16 is a cross sectional view of part of the bearing sectionaccording to a fourteenth example of the embodiment of the presentinvention.

[0042]FIG. 17 is a perspective view of the retainer used in the bearingdevice according to the fourteenth example of the embodiment of thepresent invention.

[0043]FIG. 18 is a cross sectional view of a retainer of FIG. 17.

[0044]FIG. 19 is a cross sectional view corresponding to FIG. 16.

[0045]FIG. 20 is a cross sectional view of a comparative examplecorresponding to FIG. 16.

[0046]FIG. 21 is a cross sectional view of part of a bearing deviceaccording to a fifteenth example of the embodiment of the presentinvention.

[0047]FIG. 22 is a cross sectional view of part of a bearing deviceaccording to a sixteenth example of the embodiment of the presentinvention.

[0048]FIG. 23 is a cross sectional view of part of a bearing deviceaccording to a seventeenth example of the embodiment of the presentinvention.

[0049]FIG. 24 is a cross sectional view of part of the bearing sectionaccording to the seventeenth example of the embodiment of the presentinvention.

[0050]FIG. 25 is a cross sectional view of part of the bearing sectionaccording to the eighteenth example of the embodiment of the presentinvention.

[0051]FIG. 26 is a cross sectional view of part of the bearing sectionaccording to the nineteenth example of the embodiment of the presentinvention.

[0052]FIG. 27 is a cross sectional view of part of the bearing sectionaccording to the twentieth example of the embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] The bearing device in one feature of this invention comprises: ashaft, a housing, and a double-row bearing set between the shaft andhousing such that it is pre-loaded by a fixed-position pre-loadingmethod, and where on the shaft side or housing side, there is a supportmember that supports, in the pre-loading direction, one side of the tworaces located with the gap for adjusting the pre-load. Of the two racesthat are located with the pre-load adjustment space, the race that issupported on one side in the pre-load direction by the aforementionedsupport member is called “the first race”, and the other race is called“the second race”. The term “ring” can also be used in place of “race”in the present specification.

[0054] With the bearing device of this invention, the position of thefirst race is fixed in the pre-load direction by the support member, soit is possible to reduce the width (dimension in the axial direction) ofthis first race, and to increase the width of the second race. Also, byfastening with adhesion this second race to the shaft or to the housingin a fitting relation, it is possible to obtain sufficient bondingstrength even when the width (dimension in the axial direction) of thedouble-row bearing is very small, that is 2 mm or less. The first racemay be or not be fastened with adhesion to the shaft or housing in afitting relation.

[0055] In this way, in the bearing device of this invention, of the tworaces that are located with the pre-load adjustment gap, it is desirablethat the width of the first race, that is supported in the pre-loaddirection by the aforementioned support member, be less than the widthof the other race, or second race, and that at least the second race befastened with adhesion to the shaft or to the housing in a fittingrelation.

[0056] In this case, the first race is supported by the support membereven when an external load is applied to the bearing device, and thesecond race is secured by a wide bonding surface, so there is nomovement of these races.

[0057] In a preferred embodiment of this invention, the races that arelocated with the pre-load adjustment gap are the inner rings, and thereis a ring-shaped member located in the space between the innerperipheral surface of the inner ring (first inner ring), that issupported in the pre-load direction by the aforementioned supportmember, and the shaft. In addition, the dimension in the axial direction(length) of this ring-shaped member is larger than the dimension in theaxial direction (width) of the inner ring (first inner ring), and thisring-shaped member and the support member are formed as one member, andtogether with fastening with adhesion this ring-shaped member to theshaft. Further, there is a flange that protrudes out in the radialdirection to the outside of this ring-shaped member such that the otherinner ring (second inner ring) fits with this flange.

[0058] With this bearing device, the length of the ring-shaped member isgreater than the width of the inner ring, that is supported by thesupport member, this ring-shaped member is fastened with adhesion to theshaft, and the other inner ring fits with the flange. Therefore, it ispossible to obtain sufficient bonding strength even when the width(direction in the axial direction) of the double-row bearing is verysmall, that is 2 mm or less.

[0059] Moreover, a raceway is formed on the outer peripheral surface ofthis flange, and by making the radially inner section of this flange thesecond inner ring, the second inner ring is integrated with shaft, andthe position of the second ring is securely fixed in relation to theshaft, so it is possible to obtain even more stability when an externalload is applied to the bearing device.

[0060] In another embodiment of the invention, the races that arelocated with the pre-load adjustment gap are the inner rings, and thewidth of the radially inner section of the inner ring (first inner ring)that is supported on its side in the pre-load direction by theaforementioned support member, is greater than the width of the radiallyouter section thereof, and the width of the radially inner section ofthe other ring (second inner ring) is less than the width of theradially outer section thereof, such that the outer diameter of theradially inner section of the first inner ring is equal to the innerdiameter of the radially inner section of the second inner ring, andwhere the outer peripheral surface of the radially inner section of thefirst inner ring and the inner peripheral surface of the radially innersection of the second inner ring fit together, and where there is amember located between the shaft and the double-row bearing comprising aring member that is located between the inner peripheral surface of theradially inner section of the first ring and the shaft, and a flangethat protrudes outward from one end in the lengthwise direction of thisring member, and where this ring member is fastened to the innerperipheral surface of the radially inner section of the first ring, andthe flange fits with the radially inner section of the second innerring.

[0061] With this bearing device, the radially inner section of the firstring is fastened with adhesion to the ring member over a wide bondingsurface, and the radially inner section of the second inner ring fitswith the radially inner section of the first inner ring as well asengages with the flange. Therefore, it is possible to obtain sufficientbonding strength even when the width (dimension in the axial direction)of the double-row bearing is very small, that is 2 mm or less.

[0062] The double-row ball bearing of this invention, which is setbetween the shaft and the housing such that it is pre-loaded by afixed-position pre-loading method, has the following four features:

[0063] (1) The two rows of balls are located at positions such that theyare separated from each other in the radial direction of the bearing.

[0064] (2) The first inner ring is formed such that the width of theradially inner section on the shaft side is less than the width of theradially inner section having the raceway.

[0065] (3) The second inner ring is formed such that the width of theradially inner section on the housing side is less than the width of theradially inner section having the raceway.

[0066] (4) The radially inner section of the first inner ring is locatedfurther outside in the radial direction than the radially inner sectionof the second inner ring.

[0067] With the double-row ball bearing of this invention, it ispossible to suppress vibration or run-out of the rotating shaft evenwhen the width of the bearing is greatly reduced.

[0068] In the double-row ball bearing of this invention, it is desirablethat the two rows of balls are such that the distance in the axialdirection, specifically the distance between the centers of the balls inrespective rows is less than the diameter of the balls, and that thedifference between the diameter of the pitch circle of the balls in onerow and the diameter of the pitch circle of the balls in the other rowis two times or greater than the diameter of the balls.

[0069] It is desirable that the double-row ball bearing of thisinvention have a retaining member for maintaining a pre-load adjustmentgap. By doing so, it is possible to adjust the pre-load beforeinstalling the double-row ball bearing between the shaft and thehousing.

[0070] Moreover, by press-fitting two races with a pre-load adjustmentgap, such that they can move with respect to the gap retaining member,it is possible to adjust the pre-load after the bearing has beeninstalled.

[0071] A ring member that is located between the two races with thepre-load adjustment gap, and the shaft or housing, is used as this gapretaining member.

[0072] It is also possible for the second inner ring to function as thegap retaining member by forming the width of the second inner ring suchthat it is greater than the width of first inner ring, and fitting theradially inner section of the first inner ring in the radially outersection of the second inner ring.

[0073] With the races that are deformed elastically by pressing on thesides of each race in order to pre-load the bearing, it is possible tohave separate races for each row of balls or it is possible to form theraces in a single member where the raceways are provided for both rowsof balls.

[0074]FIG. 1 is a cross-sectional drawing showing the bearing device ofa first example of the invention.

[0075] This bearing device comprises a shaft 1, a housing 2 and adouble-row ball bearing 3. The double-row ball bearing 3 is set betweenthe shaft 1 and the housing 2, such that it is pre-loaded by afixed-position pre-loading method. In this bearing device, thedouble-row ball bearing 3 has two, first and second inner rings 4, 5which are provided with a gap S for adjusting the pre-load, and two,first and second outer rings 6, 7 which are located such that they arepressed directly.

[0076] On one end in the lengthwise direction of the shaft 1, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe surface, on the shaft 1 side of this circular disk-shaped member 11,there is a support member 8 that supports the outer surface of the firstinner ring 4 (surface on the opposite side of the pre-load adjustmentgap S) in the pre-load direction. The housing 2 comprises an outerperipheral member 21 that supports the outer peripheral surface of thetwo outer rings 6, 7, and a side surface member 22 that supports theoutside (axially outer) surface of the second outer ring 7 which islocated on the outside (axially outer side) of the second inner ring 5.

[0077] The widths of the two outer rings 6, 7 of the double-row ballbearing 3 are the same to each other, and uniform throughout in theradial direction. The balls 32, 32 in the two rows of the double-rowball bearing 3 have the same ball diameter and are arranged in the sameradial location.

[0078] The widths (dimension in the axial direction) of the radiallyouter sections, having the raceways, of the two inner rings 4, 5 of thedouble-row ball bearing 3 are the same to each other, however the widthsof the radially inner sections (on the shaft 1 side) are different. Forthe first inner ring 4, the width of the radially inner section 42 isnarrower than the radially outer section 41. For the second inner ring5, the width of the radially inner section 52 is broader than theradially outer section 51. Therefore, the width of the radially innersection 52 of the second inner ring 5 is wider than the width of theradially inner section 42 of the first inner ring 4. The radially innersection 52 of the second inner ring 5 protrudes outward in the axialdirection (downward in FIG. 1) from the second outer ring 7, and entersinside the first outer ring 6.

[0079] The inner peripheral surface of the radially inner section 52 ofthe second inner ring 5 is bonded to the shaft 1. The inner peripheralsurface of the radially inner section 42 of the first inner ring 4 isnot bonded to the shaft 1. The outside surface of the first inner ring 4is supported by the support member 8. The two outer rings 6, 7 fit at afixed gap with-the outer peripheral member 21 of the housing 2.Moreover, the outside surface of the second outer ring 7 is pressed ontothe side-surface member 22 of the housing 2.

[0080] As described above, with the bearing device, the position of thefirst inner ring 4 is fixed by the support member 8, the width ofradially inner section 42 of the first inner ring 4 is much less thanthe width of the radially inner section 52 of the second inner ring 5,and the wide radially inner section 52 of the second inner ring 5 isfastened to the shaft 1 with adhesion. Accordingly, with this bearingdevice, there is no movement of the first inner ring 4 even when thewidth of the double-row ball bearing 3 is very small, that is 2 mm orless, so it is possible to obtain sufficient bonding strength withsecond inner ring 5.

[0081] The inner peripheral surface of the radially inner section 42 ofthe first inner ring 4 may be fastened to the radially outer surface ofthe shaft 1 with adhesion.

[0082]FIG. 2 is a cross-sectional drawing showing the bearing device ofa second example of this invention.

[0083] This bearing device comprises a shaft 1, a housing 2 anddouble-row ball bearing 3. The double-row ball bearing 3 is set betweenthe shaft 1 and the housing 2 such that it is pre-loaded by afixed-position pre-loading method. In this bearing device, thedouble-row ball bearing 3 has two, first and second outer rings 6, 7which are arranged with a gap S for adjusting the pre-load, and two,first and second inner rings 4, 5 which are located such that they arepressed directly to each other.

[0084] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe surface on the shaft 1 side of this circular disk-shaped member 11,there is a support member 8 for supporting the side surface of thesecond inner ring 5. The housing 2 comprises an outer peripheral member21 for supporting the outer peripheral surface of the two outer rings 6,7, and a side-surface member 23 for supporting the outside surface ofthe first outer ring 7.

[0085] Both of the two inner rings 4, 5 of the double-row ball bearing 3have the same width, and they both have a fixed width in the radialdirection. For the two rows of balls 31, 32 of the double-row ballbearing 3, the balls 31 of one row and the balls 32 of the other rowhave the same ball diameter, and they are arranged at the same positionin radial direction.

[0086] The two outer rings 6, 7 of the double-row ball bearing 3 havethe same width on the radially inner side having the raceways, however,the widths on the radially outer side (on the housing 2 side) aredifferent. For one outer ring (first outer ring) 6, the width of theradially outer section 62 is narrower than that of the radially innersection 61. For the other outer ring (second outer ring) 7, the width ofthe radially outer section 72 is greater than that of the radially innersection 71. Therefore, the width of the radially outer section 72 of thesecond outer ring 7 is wider than the radially outer section 62 of thefirst outer ring 6. The radially outer section 72 of the second outerring 7 protrudes outward in the axial direction (upward in FIG. 2) fromthe second inner ring 5.

[0087] The outer peripheral surface of the radially outer section 72 ofthe second outer ring 7 is bonded to the outer peripheral member 21 ofthe housing 2. The outer peripheral surface of the radially outersection 62 of the first outer ring 6 is not bonded to the outerperipheral member 21 of the housing 2. The outside surface (sideopposite from the pre-load adjustment space S side) of the first outerring 6 is supported by the side-surface member 22 of the housing 2.Here, this side-surface member 22 corresponds to the support member ofthis embodiment. The two inner rings 4, 5 fit at a fixed gap on theshaft 1. Moreover, the outside surface of the second inner ring 5 issupported by the support member 8.

[0088] As described above, in this bearing device, the position of thefirst outer ring 6 is fixed by the side-surface member (support member)22, the width of the radially outer section 62 of the first outer ring 6is much less than the width of the radially outer section 72 of thesecond outer ring 7, and the wide radially outer section 72 of the widesecond outer ring 7 is fastened with adhesion to the outer peripheralmember 21 of the housing 2. Accordingly, with this bearing device, thefirst outer ring 6 does not move even when the width of the double-rowball bearing 3 is very small, that is 2 mm or less, thus it is possibleto obtain sufficient bonding strength with the second outer ring 7.

[0089] The outer peripheral surface of the radially outer section 62 ofthe first outer ring 6 may be fastened with adhesion to the outerperipheral member 21 of the housing 2.

[0090]FIG. 3 is a cross-sectional drawing showing the bearing device ofa third example of the embodiment of this invention.

[0091] This bearing device comprises a shaft 1, a housing 2 anddouble-row ball bearing 3. The double-row ball bearing 3 is set betweenthe shaft 1 and the housing 2 such that it is pre-loaded by afixed-position pre-loading method.

[0092] In this bearing device, the double-row ball bearing 3 has two,first and second inner rings 4, 5 which are arranged with a gap S foradjusting the pre-load. Moreover, in this double-row ball bearing 3there is one outer ring 16, and there are two raceways formed on theinner peripheral surface of this outer ring 16. For the two rows ofballs 31, 32 of the double-row ball bearing 3, both rows of balls 31, 32have the same ball diameter, and they are arranged at the same positionin the radial direction.

[0093] At one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe surface of the shaft 1 side of this circular disk-shaped member 11,there is a support member 8 for supporting the outside surface (the sidesurface opposite from the space S side) of the first inner ring 4 in thepre-load direction. Moreover, the housing 2 comprises an outerperipheral member 21 for supporting the outer peripheral surface of theouter ring 16, and a side member 22 for supporting the outside surfaceof the outer ring 16.

[0094] Of the two inner rings 4, 5 of the double-row ball bearing 3, theinner diameter of the first inner ring 4 is formed such that it islarger than the outer diameter of the shaft 1, and the inner diameter ofthe second inner ring 5 is formed such that it is nearly the same as theouter diameter of the shaft 1. In addition, the second inner ring 5comprises a radially outer section 51, that has the same width as thefirst inner ring 4, and a radially inner section 52, that has a widththat is substantially equal to the length of the shaft 1. This radiallyinner section 52 of the second inner ring 5 protrudes in the axialdirection into the first inner ring 4 side (downward in FIG. 3). Inother words, the first inner ring 4 is located such that the secondinner ring 5 is surrounded by the inner peripheral surface of the firstinner ring 4. Also, the inner peripheral surface of the second innerring 5 fits entirely over the lengthwise direction of the shaft 1.

[0095] The inner peripheral surface of the radially inner section 52 ofthe second inner ring 5 is bonded to the shaft. The outer peripheralsurface of the radially inner section 52 of the second inner ring 5 isnot bonded to the inner peripheral surface of the first inner ring 4.The outside (axially outer) surface of the first inner ring 4 issupported by the support member 8. Moreover, the outer peripheralsurface of the outer ring 16 fits to the outer peripheral member 21 ofthe housing 2 with a fixed gap, and the outer surface of the axiallyouter ring 16 is pressed to the side-surface member 22 of the housing 2.

[0096] As described above, in this bearing device, the position of thefirst inner ring 4 is fixed by the support member 8, and the radiallyinner section 52 of the second inner ring 5, with a width equal to thelength of the shaft 1, is fastened to the shaft 1 with adhesion.Moreover, with this bearing device, there is no movement of the firstinner ring 4 even when the width of the double-row ball bearing 3 isvery small, that is 2 mm or less, thus it is possible to obtainsufficient bonding strength with the second inner ring 5.

[0097] Also, with this bearing device, two raceway grooves are formed inthe one outer ring 16, so that is particularly effective in making itpossible to reduce the relative angle between the outer raceway groovesin both rows, and improving the vibration precision.

[0098] The inner peripheral surface of the radially inner section 42 ofthe first ring 4 may be fastened with adhesion to the outer peripheralsurface of the second inner ring 5.

[0099]FIG. 4 is a cross-sectional drawing showing the bearing device ofa fourth example of this invention.

[0100] This bearing device comprises a shaft 1, a housing 2, adouble-row ball bearing 3, and a ring-shaped member 12. The double-rowball bearing 3 is set between the shaft 1 and the housing 2 by way ofthe ring-shaped member 12 such that it is pre-loaded by a fixed-positionpre-loading method. In the bearing device, the double-row ball bearing 3has first and second inner rings 4, 5 which are arranged with a gap Sfor adjusting the pre-load, and first and second outer rings 6, 7 whichare arranged such that they are directly pressed.

[0101] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe surface on the shaft 1 side of this circular disk-shaped member,there is a support member 8 for supporting the outside surface (sidesurface opposite the space S) of the first inner ring 4 in the pre-loaddirection. The housing 2 comprises an outer peripheral member 21 forsupporting the outer peripheral surface of the two outer rings 6, 7, andan side-surface member 22 for supporting the outside surface of thesecond outer ring 7.

[0102] The two rows of balls 31, 32 of the double-row ball bearing 3 arearranged such that they are separated from each other in the radialdirection (left and right directions in FIG. 4) of the bearing. One row(first) of balls 31 is located further on the outside in the radialdirection of the bearing than the other row (second row) of balls 32.The difference between the diameter of the pitch circle of the firstballs 31 and the diameter of the pitch circle of the second balls 32 isapproximately four times the diameter of the balls 31, 32. The two rowsof balls 31, 32 are arranged in the axial direction such that they arelocated at position separated by just the radius of the balls 31, 32with respect to the distance between the centers of the balls 31, 32.

[0103] The first outer ring 6 has a normal outer ring shape, however,the second outer ring 7 comprises a radially inner section 73 having araceway, a radially intermediate section 74 that is located at theposition of the first row of balls 31 in the radial direction, and aradially outer section 75 that is pressed by one side surface of thefirst outer ring 6. The width of the first outer ring 6 is formed suchthat it is larger than the width of the radially outer section 75 of thesecond outer ring 7.

[0104] The second inner ring 5 has a normal inner ring shape, howeverthe first inner ring 4 comprises a radially outer section 41 having araceway, and an radially inner section 42 on the shaft 1 side. The widthof the radially inner section 42 of the first inner ring 4 is formedsuch that it is narrower than the width of the radially outer section41. The width of the second inner ring 5 is formed such that it islarger than the width of the radially inner section 42 of the firstinner ring 4.

[0105] The radially inner section 42 of the first inner ring 4, theradially inner section 73 of the second outer ring 7, the second row ofballs 32, and the second inner ring 5 are arranged such that they faceeach other with a fixed gap therebetween. Moreover, the first outer ring6 and the radially outer section 75 of the second outer ring 7 arearranged such that they come in contact with each other in the axialdirection. Also, a fixed gap is formed between the radially outersection 41 of the first inner ring 4 and the outer peripheral surface ofthe radially inner section 73 of the second outer ring 7, and betweenthe radially the radially outer section 41 of the first inner ring 4 andthe inside (axially inner) surface of the radially intermediate section74 of the second outer ring 7, respectively.

[0106] The inner peripheral surface of the second inner ring 5 is bondedto the ring-shaped member 12 for fastening. The inner peripheral surfaceof the radially inner section 42 of the first inner ring 4 is not bondedto the ring-shaped member 12. The ring-shaped member 12 is bonded to theshaft 1 for fastening. The outer surface of the first inner ring 4 issupported by the support member 8. The outer peripheral surface of thetwo outer rings 6, 7 fits with a fixed gap to the outer peripheralmember 21 of the housing 2. Moreover, the outer surface of the secondouter ring 7 is pressed by the side-surface member 22 of the housing 2.The outer peripheral surface of the two outer rings 6, 7 may be fastenedto the outer peripheral member 21 of the housing 2 by thermal shrinkagefitting.

[0107] As described above, in this bearing device, the position of thefirst inner ring 4 is fixed by the support member 8, the width of theradially inner section 42 of the first inner ring 4 is less than thewidth of the radially inner section 52 of the second inner ring 5, andthe wide radially inner section 52 of the wide second inner ring 5 isfastened to the ring-shaped member 12 with adhesion. Also, with thisbearing device, there is no movement of the first inner ring 4 even whenthe width of the double-row ball bearing 3 is very small, that is 2 mmor less, thus it is possible to obtain sufficient bonding strength withthe second inner ring 5.

[0108] In addition, with this bearing device, by separating thelocations of the two rows of balls 31, 32 from each other in the radialdirection of the bearing and by placing the first inner ring 4 and thesecond outer ring 7 such that the radially outer section 41 of the firstinner ring 4 is further outside in the radial direction than theradially inner section 73 of the outer ring 7, it is possible to makethe width of the double-row ball bearing less than in the cases of firstand third examples. Also, since there is a ring-shaped member 12 betweenthe inner rings 4, 5 and the shaft 1, it is possible to adjust thepre-load before installing the shaft 1.

[0109] The inner peripheral surface of the radially inner section 42 ofthe first inner ring 4 may be fastened with adhesion to the ring-shapedmember 12.

[0110]FIG. 5 is a cross-sectional drawing showing the bearing device ofa fifth example of this invention.

[0111] This bearing device comprises a shaft 1, a housing 2 anddouble-row ball bearing 3. The double-row ball bearing 3 is set betweenthe shaft 1 and the housing 2 such that it is pre-loaded by afixed-position pre-loading method. This double-row ball bearing 3 hasfirst and second inner rings 4, 5 and first and second outer rings 6, 7,where the first inner ring 4 is arranged such that the second inner ring5 is generally surrounded by the inner peripheral surface at the firstinner ring 4. The width of the second inner ring 5 is equal to thelength of the shaft 1, and the width of the radially inner section 42 ofthe first inner ring 4 is ⅓ the width of the second inner ring 5.

[0112] The two rows of balls 31, 32 of the double-row ball bearing 3 arelocated such that they are separated from each other in the radialdirection of the bearing. The balls 31 of one row (first row) is locatedfurther outside in the radial direction of the bearing than the balls 32of the other row (second row). The difference in the diameter betweenthe pitch circle of the balls 31 and the pitch circle of the balls 32 isapproximately 4 times the diameter of the balls 31, 32. The two rows ofballs 31, 32 are arranged in the axial direction such that they arelocated at positions separated by just the radius of the balls 31, 32with respect to the distance between the centers of the balls 31, 32.

[0113] The first outer ring 6 has a normal outer ring shape, however,the second outer ring 7 comprises a radially inner section 73 having araceway, a radially intermediate section 74 that is located at theposition of the first row of balls 31 in the radial direction, and aradially outer section 75 that is pressed by the side surface of thefirst outer ring 6. The width of the first outer ring 6 is formed suchthat it is larger than the width of the radially outer section 75 of thesecond outer ring 7.

[0114] The second inner ring 5 has a normal inner ring shape, however,the first inner ring 4 comprises a radially outer section 41 having araceway, and a radially inner section 42 on the shaft 1 side. The widthof the radially inner section 42 of the first inner ring 4 is formedsuch that it is narrower than the width of the radially outer section41. The width of the second inner ring 5 is formed such that it islarger than the width of the radially inner section of the first innerring 4.

[0115] The radially inner section 42 of the first inner ring 4, theradially inner section 73 of the second outer ring 7 and the second rowof balls 32 are arranged such that they face each other though a fixedgap therebetween. The first outer ring 6 and the radially outer section75 of the second outer ring 7 are arranged such that they come incontact with each other in the axial direction. In other words, the twoouter rings 6, 7 are arranged such that they are directly pressed toeach other.

[0116] A gap S for adjusting the pre-load is axially formed between theradially inner section 42 of the first inner ring 4 and the radiallyinner section 73 of the second outer ring 7. Moreover, a fixed gap isformed between the radially outer section 41 of the first inner ring 4and the outer peripheral surface of the radially inner section 73 of thesecond outer ring 7, and between the radially outer section 41 of thefirst inner ring 4 and the inside surface of the radially intermediatesection 74 of the outer ring 7, respectively.

[0117] On one end in the lengthwise direction of the shaft 1 there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe surface on the shaft 1 side of this circular disk-shaped member 11,there is a support member 8 that supports the outer surface of the firstinner ring 4 (surface on the opposite side of the gap S) in the pre-loaddirection. The housing 2 comprises an outer peripheral member 21 thatsupports the outer peripheral surface of the two outer rings 6, 7, and aside-section member 22 that supports the outside surface of the secondouter ring 7.

[0118] The inner peripheral surface of the second inner ring 5 is bondedto the shaft 1 across the entire length of the shaft 1. The innerperipheral surface of the radially inner section 42 of the first innerring 4 is not bonded to the outer peripheral surface of the second innerring 5. The outside surface of the first inner ring 4 is supported bythe support member 8. The two outer rings 6, 7 fit on the outerperipheral member 21 of the housing 2 with a fixed gap therebetween.Moreover, the outside surface of the second outer ring 7 is pressed bythe side-surface section 22 of the housing 2.

[0119] As described above, in this bearing device, the position of thefirst inner ring 4 is fixed by the support member 8, and the secondinner ring 5 is fastened with adhesion to the shaft 1 along its widthwhich is equal to the length of the shaft 1. Also, there is no movementof the first inner ring 4 even when the width of the double-row ballbearing 3 is very small, that is 2 mm or less, thus it is possible toobtain sufficient bonding strength with the second inner ring 5.

[0120] In addition, with this bearing device, by shifting the locationof the two rows of balls 31, 32 in the radial direction of the bearingand placing the first inner ring 4 and second outer ring 7 such that theradially outer section 41 of the inner ring 4 is further outside in theradial direction than the radially inner peripheral section 73 of theouter ring 7, the width of the double-row ball bearing 3 becomes smallerthan in the first to third examples. Moreover, since the first innerring 4 is on the outside of the second inner ring 5, it is possible toadjust there-load before attaching it to the shaft 1.

[0121] The inner surface of the radially inner section 42 of the firstinner ring may be fastened to the outer peripheral surface of the secondinner ring 5.

[0122]FIG. 6 is a cross-sectional drawing showing the bearing device ofa sixth example of the embodiment of this invention.

[0123] This bearing device comprises a shaft 1, a housing 2, adouble-row ball bearing 3, and a fourth member 9. The double-row ballbearing 3 is set between the fourth member 9, the shaft 1 and thehousing 2 such that it is pre-loaded by a fixed-position pre-loadingmethod.

[0124] In this bearing device, the double-row ball bearing 3 has firstand second inner rings 4, 5 which are arranged with a gap S foradjusting the pre-load. The width (dimension in the axial direction) ofthe first inner ring 4 is the same in the radial direction, however thesecond inner ring 5 comprises a radially outer section 51 that has thesame width (dimension in the axial direction) as the first inner ring 4,and a radially inner section 52 that is narrower than this. Moreover, inthis double-row ball bearing 3 there is one outer ring 16, and there aretwo raceways formed on the inner peripheral surface of this outer ring16. For the two rows of balls 31, 32 of the double-row ball bearing 3,both rows of balls 31, 32 have the same ball diameter, and they arearranged at the same position in the radial direction.

[0125] The housing 2 comprises an outer peripheral member 21 forsupporting the outer peripheral surface of the outer ring 16, and aside-surface member 22 for supporting the outside surface of the outerring 16 on the side of the second inner ring 5.

[0126] The fourth member 9 comprises a ring-shaped member 12 that islocated between the inner peripheral surfaces of the inner rings 4, 5and the shaft 1, and a circular disk-shaped member 11 that is located onone end of the shaft 1 (on the side of the first inner ring 4) such thatit is integrated with the shaft 1. On the shaft 1 side of this circulardisk-shaped member 11, there is a support member. 8 that is formed suchthat it supports the outside surface (surface opposite to the gap S) ofthe first inner ring 4 in the pre-load direction.

[0127] On the other end (on the side of the second inner ring 5) of theshaft 1 in the lengthwise direction, there is a flange 18 that protrudesoutward in the radial direction than the ring-shaped member 12. Thewidth of the radially inner section 52 of the second inner ring 5 isless than the width of the radially outer peripheral section 51 by justthe amount of the thickness of the flange 18. Also, the flange 18 andthe outside surface of the radially inner section 52 of the second innerring 5 come in contact with each other. There is a fixed gap between theinner peripheral surface of the radially outer section 51 of the secondinner ring 5 and the outer peripheral surface of the flange 18.Moreover, there is a fixed gap between the axial end surface on theflange 18 side of the ring-shaped member 15 and the flange 18.

[0128] The dimension (length) in the axial direction of the innerperipheral surface of the ring-shaped member 12 is two times or morethan the dimension (width) in the axial direction of the first innerring 4. This ring-shaped member 12 is bonded to the shaft 1. The innerperipheral surface of the radially inner section 52 of the second innerring 5 is not bonded to the ring-shaped member 12. The inner peripheralsurface of the first inner ring 4 is not bonded to the ring-shapedmember 12. The outside surface of the first inner ring 4 is supported bythe support member 8. The outer ring 16 fits with the radially outersection 21 of the housing 2. Moreover, the outside surface of the outerring 16 is pressed to the side-surface member 22 of the housing 2.

[0129] As described above, in this bearing device, the length of theinner peripheral surface of the ring-shaped member 12 is greater thanthe width of the first inner ring 4, and this ring-shaped member 12 isfastened with adhesion to the shaft 1. Moreover, the position of thesecond inner ring 5 is fixed by the flange 8, and the position of thefirst inner ring 4 is fixed by the support member 8. Also, with thisbearing device, there is no movement of the first inner ring 4 andsecond inner ring 5 even when the width of the double-row ball bearing 3is very small, that is 2 mm or less, thus it is possible to obtainsufficient bonding strength with the ring-shaped member 12.

[0130] The inner peripheral surface of the radially inner section 52 ofthe second inner ring 5 and the peripheral inner surface of the firstinner ring 4 may be bonded to the outer peripheral surface of thering-shaped member 12.

[0131]FIG. 7 is a cross-sectional drawing showing the bearing device ofa seventh example of this invention.

[0132] This bearing device comprises a shaft 1, a housing 2, adouble-row ball bearing 3, and a fourth member 9. The double-row ballbearing 3 is set between the fourth member 9, the shaft 1 and thehousing 2 such that it is pre-loaded by a fixed-position pre-loadingmethod. In this bearing device, there is a flange 19 at one end of theshaft 1 in the lengthwise direction, and by forming a raceway 53 on theouter peripheral surface of this flange 19, the function of an innerrace is given to the radially outer section 19 a of this flange 19.

[0133] This double-row ball bearing 3 further comprises an inner ring 4(first inner ring) having a width that is the same dimension as thethickness (dimension in the axial direction) as the flange 19, and anouter ring 16 that has two raceways formed around its inner peripheralsurface. This inner ring 4 and the radially outer section 19 a of theflange 19, that functions as another inner ring, are arranged with a gapS for adjusting the pre-load.

[0134] Moreover, for the two rows of balls 31, 32 of the double-row ballbearing 3, both rows of balls 31, 32 have the same ball diameter, andthey are arranged at the same position in the radial direction.

[0135] The housing 2 comprises an outer peripheral member 21 forsupporting the outer peripheral surface of the outer ring 16, and aside-surface member for supporting the outside surface of the outer ring16 on the side of the second inner ring 5.

[0136] The fourth member 9 comprises a ring-shaped member 12 that islocated between the inner peripheral surface of the inner ring 4 and theshaft 1, and a circular disk-shaped member 11 that is located on one endof the shaft 1 (on the side of the inner ring 4) such that it isintegrated with the shaft 1. On the shaft 1 side of this circulardisk-shaped member 11, there is a support member 8 that is formed suchthat it supports the outside surface (the surface opposite to the gap S)of the inner ring 4 in the pre-load direction.

[0137] The dimension (length) in the axial direction of the innerperipheral surface of the ring-shape member 12 is greater than thedimension (width) in the axial direction of the first inner ring 4 byjust the amount of the thickness of the circular disk-shaped member 11.The ring-shaped member 12 is bonded to the shaft 1. The inner peripheralsurface of the inner ring 4 is not bonded to the ring-shaped member 12.The outside surface of the inner ring 4 is supported by the supportmember 8. There is a fixed gap between the axial end surface on theflange 19 side of the ring-shaped member 12 and the flange 19. The outerperipheral surface of the outer ring 16 fits with the outer peripheralmember 21 of the housing 2. Moreover, the outside surface of the outerring 16 is pressed to the side-surface member 22 of the housing 2.

[0138] As described above, in this bearing device, the length of theinner peripheral surface of the ring-shaped member 12 is greater thanthe width of the first inner ring 4, and this ring-shaped member 12 isfastened with adhesion to the shaft 1. Also, by having the radiallyouter section 19 a of the flange 19 function as a second inner ring, theposition of the second inner ring is fixed by the shaft 1, and theposition of the first inner ring 4 is fixed by the support member 8.Moreover, with this bearing device, there is no movement of the firstinner ring 4 and the second inner ring (radially outer section 19 a ofthe flange 19) even when the width of the double-row ball bearing 3 isvery small, that is 2 mm or less, thus it is possible to obtainsufficient bonding strength with the ring-shaped member 12.

[0139] In addition, with this bearing device, since the radially outersection 19 a of the flange 19 on the shaft 1 functions as the secondinner ring 5, stability of the bearing is increased when an externalload is applied, when compared with the bearing device of the sixthexample.

[0140] The inner peripheral surface of the inner ring 4 may be bonded tothe outer peripheral surface of the ring-shaped member 15.

[0141]FIG. 8 is a cross-sectional drawing showing the bearing device ofan eighth example of this invention.

[0142] This bearing device comprises a shaft 1, a housing 2, adouble-row ball bearing 3, and a fourth member 9. The double-row ballbearing 3 is set, through the fourth member 9, between the shaft 1 andthe housing 2 such that it is pre-loaded by a fixed-position pre-loadingmethod. In this bearing device, the double-row ball bearing 3 has firstand second inner rings 4, 5 which are arranged with a gap S foradjusting the pre-load.

[0143] Moreover, in this double-row ball bearing 3 there is one outerring 16, and there are two raceways formed on the inner peripheralsurface of this outer ring 16. For the two rows of balls 31, 32 of thedouble-row ball bearing 3, both rows of balls 31, 32 have the same balldiameter, and they are arranged at the same position in the radialdirection.

[0144] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe shaft 1 end of this circular disk-shaped member 11, there is asupport member 8 that is formed such that it supports the outsidesurface (surface opposite the gap S) of the first inner ring 4 in thepre-load direction. The housing 2 comprises an outer peripheral member21 for supporting the outer peripheral surface of the outer ring 16, anda side-surface member 22 for supporting the outside surface of the outerring 16.

[0145] The fourth member 9 comprises a ring-shaped member 12 that fitsentirely around the length of the shaft 1, and a flange 18 that islocated at one end in the lengthwise direction of the ring-shaped member12 and is integrated with the ring-shaped member 12.

[0146] The two inner rings 4, 5 of the double-row ball bearing 3 havethe same width (dimension in the axial direction) on the radially innersection having raceways, however, the widths of the radially innersection (on the shaft 1 side) differ. The width of the radially innersection 42 of the first inner ring 4 is wider than the width of theradially outer section 41. The width of the radially inner section 52 ofthe second inner ring 5 is narrower than the width of the radially outersection 51. The outer diameter of the radially inner section 42 of thefirst inner ring 4 is formed such that it is the same as the innerdiameter of the radially inner section 52 of the second inner ring 5.

[0147] The inner diameter of the radially inner section 42 of the firstinner ring 4 is formed such that it is the same as the outer diameter ofthe ring-shaped member 12. The inner diameter of the radially outersection 51 of the second inner ring 5 is formed such that it is greaterthan the outer diameter of the flange 18. The flange 18 comes in contactwith the outside surface of the radially inner section 52 of the secondinner ring 5.

[0148] The outer peripheral surface of the radially inner section 42 ofthe first inner ring 4 is not bonded to the inner peripheral surface ofthe radially inner section 52 of the second inner ring 5. The innerperipheral surface of the radially inner section 42 of the first innerring 4 is bonded to the outer peripheral surface of the ring-shapedmember 12. There is a fixed gap between the inner peripheral surface ofthe radially outer section 51 of the second inner ring 5 and the outerperipheral surface of the flange 18. There is a fixed gap between theradially inner section 42 of the first inner ring 4 and the flange 18.

[0149] The outside surface of the first inner ring 4 is supported by thesupport member 8. The outer ring 16 fits with the outer peripheralmember 21 of the housing 2. Also, the outside surface of the outer ring16 is pressed to the side-surface member 22 of the housing 2.

[0150] As described above, in this bearing device, the position of thesecond inner ring 5 is fixed by the flange 18, and the position of thefirst inner ring 4 is fixed by the support member 8. Also, the wideradially inner section 42 of the first inner ring 4 is fastened withadhesion to the ring-shaped member 12. Moreover, with this bearingdevice, there is no movement on the first inner ring 4 or second innerring 5 even when the width of the double-row ball bearing 3 is verysmall, that is 2 mm or less, thus it is possible to obtain sufficientbonding strength with the ring member 12.

[0151] In addition, with this bearing device, since the ring-shapedmember 12 is located between the inner rings 4, 5 and the shaft 1, it ispossible to adjust the pre-load before attachment to the shaft 1.

[0152] The inner peripheral surface of the radially inner section 52 ofthe second inner ring 5 may be fastened with adhesion to the outerperipheral surface of the radially inner section 42 of the first innerring 4.

[0153]FIG. 9 is a cross-sectional drawing showing the bearing device ofa ninth example of the embodiment of this invention.

[0154] This bearing device comprises a shaft 1, a housing 2, adouble-row ball bearing 3, and a ring-shaped member 12. The double-rowball bearing 3 is set between the shaft 1 and the housing 2 by way ofthe ring-shaped member 12 such that it is pre-loaded by a fixed-positionpre-loading method. In this bearing device, the double-row ball bearing3 has first and second inner rings 4, 5 which are arranged with a gap Sfor adjusting the pre-load, and first and second outer rings 6, 7 whichare located such that they are pressed directly to each other.

[0155] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe shaft 1 side of this circular disk-shaped member 11, there is asupport member 8 that is formed such that it supports the outsidesurface (surface opposite the gap S) of the first inner ring 4. Thehousing 2 comprises an outer peripheral member 21 for supporting theouter peripheral surface of the two outer rings 6, 7, and a side-surfacemember 22 for supporting the outside surface of the second outer ring 7.

[0156] The two inner rings 4, 5 of the double-row ball bearing 3 havethe same width, and are formed such that they have a constant width inthe radial direction. The two outer rings 6, 7 of the double-row ballbearing 3 have the same width, and are formed such that they have aconstant width in the radial direction. The two rows of balls 31, 32 ofthe double-row ball bearing 3 are such that one row of balls 31 and theother row of balls 32 have the same ball diameter and are located at thesame position in the radial direction.

[0157] The inner peripheral surface of the second inner ring 5 is fixedby pressure-fitting or by pressure-fitting and adhesion into thering-shaped member 12. The inner peripheral surface of the first innerring 4 is not bonded to the ring-shaped member 12. The outside surfaceof the first inner ring 4 is supported by the support member 8. The twoouter rings 6, 7 fit with the outer peripheral member 21 of the housing2. Also, the outside surface of the second outer ring 7 is pressed tothe side-surface member 22 of the housing 2.

[0158] As described above, in this bearing device, the position of thefirst inner ring 4 is fixed by the support member 8, and the innerperipheral surface of the second inner ring 5 is fastened with adhesionto the shaft 1. The inner peripheral surface of the first inner ring 4may be bonded to the ring-shaped member 12. Moreover, since thering-shaped member 12 is located between the inner rings 4,5 and theshaft 1, it is possible to adjust the pre-load before attachment to theshaft 1.

[0159]FIG. 10 is a cross-sectional drawing showing a double-row ballbearing device of a tenth example of this invention.

[0160] The double-row ball bearing 3 comprises first and second innerrings 4, 5 and first and second outer rings 6, 7, and is set between theshaft 1 and the housing 2 such that it is pre-loaded by a fixed-positionpre-loading method.

[0161] The two rows of balls 31, 32 of the double-row ball bearing 3 arelocated such that they are displaced from each other in the radialdirection of the bearing. The ball diameter of the balls 31 of one rowis the same as that of the balls 32 of the other row. One row (firstrow) of balls 31 is located further outside in the radial direction ofthe bearing than the other row (second row) of balls 32. The differencebetween the diameter of the pitch circle of the first balls 31 and thediameter of the pitch circle of the second balls 32 is approximately 4times the diameter of the balls 31, 32. The two rows of balls 31, 32 arelocated such that the distance between the centers of the balls 31, 32separated in the axial direction is equal to the radius of the balls 31,32.

[0162] The first outer race 6 has a normal outer ring shape, however,the second outer race 7 comprises a radially inner section 73 having araceway, a radially intermediate section 74 that is located in theradial direction in the position of the first row of balls 31, and aradially outer section 75 that is located such that it faces the insidesurface of the first outer ring 6. The second outer ring 7 is formedsuch that the width of the radially outer section 75 is less than thewidth of the radially inner section 73.

[0163] Moreover, the width of the first outer ring 6 is formed such thatit is larger than the width of the radially outer section 75 of thesecond outer ring 7. There is a seal 90 located between the insidesurface of the first outer ring 6 and the radially outer section 75 ofthe second outer ring 7.

[0164] The second inner ring 5 has a normal inner ring shape, however,the first inner ring 4 comprises a radially outer section 41 having araceway, and a radially inner section 42 on the shaft 1 side. The firstinner ring 4 is formed such that the width of the radially inner section42 is less than the width of the radially outer section 41, and thedimension of the radially inner section 42 in the radial direction islarger than the radially outer section 41.

[0165] The radially inner section 42 of the first inner ring 4 and thesecond inner ring 5 are arranged with a gap S for adjusting thepre-load, and they are arranged such that they face each other in theaxial direction. The first inner ring 4 and the second inner 5 have thesame inner diameter, and are both pressure fitted into the ring-shapedmember (gap-retaining member) 12. This ring-shaped member 12 fits overthe shaft 1.

[0166] The radially outer section 41 of the first inner ring 4 islocated further outside in the radial direction than the radially innersection 73 of the second outer ring 7. There is a fixed gap forpreventing interference between the radially outer section 41 of thefirst inner ring 4 and the outer peripheral surface of the radiallyinner section 73 of the second outer ring 7.

[0167] There is a fixed gap for preventing interference in the axialdirection between the radially inner section 42 of the first inner ring4 and the second row of balls 32. There is a fixed gap for preventinginterference in the axial direction between the radially intermediatesection 74 of the second outer ring 7 and the first row of balls 31.Moreover, there is a seal 90 located in this gap between the radiallyintermediate section 74 and the balls 31. In addition, there is a fixedgap for preventing interference in the axial direction between theradially outer section 41 of the first inner ring 4, and the radiallyintermediate section 74 of the second outer ring 7.

[0168] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe shaft 1 side of this circular disk-shaped member 11, there is asupport member 8 that is formed such that it supports the inside surfaceof the ring-shaped member 12. The housing 2 comprises an outerperipheral member 21 for supporting the outer peripheral surface of thetwo outer rings 6, 7, and a side-surface member 22 for supporting theoutside surface of the second outer ring 7.

[0169] As described above, with this double-row ball bearing, theposition of the two rows of balls 31, 32 are displaced in the radialdirection of the bearing, and by arranging the first inner ring 4 andsecond outer ring 7 such that the radially outer section 41 of the innerring 4 is placed further outside in the radial direction than theradially inner section 73 of the outer ring 7, it is possible tosuppress vibration or run-out of the rotating shaft and decrease thewidth of the double-row ball bearing more than the bearing shown in FIG.14.

[0170] Moreover, with this double-row ball bearing, the radially innersection 42 of the first inner ring 4 and the second inner ring 5 arefitted in the ring-shaped member 12, so it is possible to adjust thepre-load before installation on the shaft 1. In addition, the double-rowball bearing can be delivered already pre-loaded. Also, this double-rowball bearing can be easily installed on the shaft 1.

[0171]FIG. 11 is a cross-sectional drawing showing a double-row ballbearing device of an eleventh example of this invention.

[0172] The double-row ball bearing 3 comprises first and second innerrings 4, 5 and first and second outer rings 6, 7, and is set between theshaft 1 and the housing 2 such that it is pre-loaded by a fixed-positionpre-loading method.

[0173] The two rows of balls 31, 32 of the double-row ball bearing 3 arelocated such that they are displaced from each other in the radialdirection of the bearing. The ball diameter of the balls 31 of one rowis the same as that of the balls 32 of the other row. One row (firstrow) of balls 31 is located further outside in the radial direction ofthe bearing than the other row (second row) of balls 32. The differencebetween the diameter of the pitch circle of the first balls 31 and thediameter of the pitch circle of the second balls 32 is approximately 4times the diameter of the balls 31, 32. The two rows of balls 31, 32 arelocated such that the distance between the centers of the balls 31, 32separated in the axial direction is equal to the radius of the balls 31,32.

[0174] The second inner ring 5 has a normal inner ring shape, however,the first inner ring 4 comprises a radially inner section 43 having araceway, a radially intermediate section 44 that is located at the sameposition in the radial direction as the position of the second row ofballs 32, and a radially inner section 45 that is located such that itfaces the inside surface of the second inner ring 5. The first innerring 4 is formed such that the widths of the radially inner section 45and radially intermediate section 44 are less than the width of theradially inner section 43. Also, the width of the second inner ring 5 isformed such that it is larger than the width of the radially innersection 45 of the first inner ring 4.

[0175] The first outer ring 6 has a normal outer ring shape, however,the second outer ring 7 comprises a radially inner section 71 having araceway, and a radially outer section 72 on the housing side 2. Thesecond outer ring 7 is formed such that the width of the radially outersection 72 is less than the width of the radially inner section 71, andthat the dimension of radially outer section 72 in the radial directionis larger than that of the radially inner section 71.

[0176] The radially outer section 72 of the second outer ring 7 and thefirst outer ring 6 face each other and arranged with a gap S foradjusting the pre-load. The second outer ring 7 and the first outer ring6 have the same outer diameter, and they are both fitted in thering-shaped member (gap retaining member) 12. This ring-shaped member 12fits in the housing 2.

[0177] The radially inner section 43 of the first inner ring 4 islocated further outside in the radial direction than the radially innersection 71 of the second outer ring 7. A fixed gap for preventinginterference is formed between the radially inner section 43 of theinner ring 4 and the radially inner section 71 of the second outer ring7.

[0178] A fixed gap for preventing interference is formed in the axialdirection between the radially intermediate section 44 of the firstinner ring 4 and the second row of balls 32. Also, there is a seal 90 inthis gap between the radially intermediate section and the balls 32. Afixed gap for preventing interference is formed in the axial directionbetween the radially outer section 72 of the second outer ring 7 and thefirst row of balls 31. Furthermore, a fixed gap for preventinginterference is formed in the axial direction between the radially innersection 71 of the second outer ring 7 and the radially intermediatesection 44 of the first inner ring 4.

[0179] A seal 91 is located between the radially intermediate section 44of the first inner ring 4 and the second row of balls 32. The outer edgeof this seal 91 is fixed to the side surface of the radially innersection 71 of the second outer ring 7. There is a seal 92 locatedbetween the radially outer section 72 of the second outer ring 7 and thefirst row of balls 31. The outer peripheral edge of this seal 92 isfixed to the side surface of the first outer ring 6.

[0180] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe shaft 1 side of this circular disk-shaped member 11, there is asupport member 8 that is formed such that it supports the side surfaceof the radially inner section 45 of the inner ring 4. Moreover, thehousing 2 comprises an outer peripheral member 21 for supporting theoutside peripheral surface of the ring-shaped member 12, and aside-surface member 22 for supporting the outside surface of thering-shaped member 12.

[0181] As described above, with this double-row ball bearing, theposition of the two rows of balls 31, 32 are displaced in the radialdirection of the bearing, and by arranging the first inner ring 4 andsecond outer ring 7 such that the radially inner section 43 of the innerring 4 is located further outside in the radial direction than theradially inner section 71 of the outer ring 7, it is possible tosuppress vibration or run-out of the rotating shaft and decrease thewidth of the double-row ball bearing.

[0182] Moreover, with this double-row ball bearing, the radially outersection 72 of the second outer ring 7 and the first outer ring 6press-fit in the ring-shaped member 12, so that it is possible to adjustthe pre-load before installation on the housing 2. In addition, thedouble-row ball bearing can be delivered already pre-loaded. Also, thisdouble-row ball bearing can be easily installed in the housing 2.

[0183]FIG. 12 is a cross-sectional drawing showing a double-row ballbearing device of a twelfth example of this invention.

[0184] The double-row ball bearing 3 comprises first and second innerrings 4, 5 and first and second outer rings 6, 7, and is set between theshaft 1 and the housing 2 such that it is pre-loaded by a fixed-positionpre-loading method.

[0185] The two rows of balls 31, 32 of the double-row ball bearing 3 arelocated such that they are displaced from each other in the radialdirection of the bearing. The ball diameter of the balls 31 of one rowis the same as that of the balls 32 of the other row. One row (firstrow) of balls 31 is located further outside in the radial direction ofthe bearing than the other row (second row) of balls 32. The differencebetween the diameter of the pitch circle of the first balls 31 and thediameter of the pitch circle of the second balls 32 is approximately 4times the diameter of the balls 31, 32. The two rows of balls 31, 32 arearranged such that the distance between the centers of the balls 31, 32separated in the axial direction is equal to the radius of the balls 31,32.

[0186] The first outer ring 6 has a normal outer ring shape, however,the second outer ring 7 comprises a radially inner section 73 having araceway, a radially intermediate section 74 that is located at the sameposition in the radial direction as the position of the first row ofballs 31, and a radially outer section 75 that is pressed to the sidesurface of the first outer ring 6. The second outer ring 7 is formedsuch that the width of the radially outer section 75 is less than thewidth of the radially inner section 73. Also, the width of the firstouter ring 6 is formed such that it is greater than the width of theradially outer section 75 of the second outer ring 7. The first outerring 6 and the radially outer section 75 of the second outer ring 7 arearranged such that their side surfaces come in contact with each other.

[0187] The second inner ring 5 has a normal inner ring shape, however,the first inner ring 4 comprises a radially outer section 41 having araceway, and a radially inner section 42 on the shaft 1 side. The firstinner ring 4 is formed such that the width of the radially inner section42 is less than the width of the radially outer section 41, and that thedimension of the radially inner section 42 in the radial direction isgreater than that of the radially outer section 41.

[0188] Moreover, the width of the second inner ring 5 is nearly the sameas the length of the shaft 1, and the width of the radially innersection 42 of the first inner ring 4 is about ⅓ the width of the secondinner ring 5. The radially inner section 42 of the first inner ring 4fits around the outer peripheral surface of the second inner ring 5. Inother words, the second inner ring 5 also functions as a gap retainingmember.

[0189] The radially outer section 41 of the first inner ring 4 isarranged such that it is further outside in the radial direction thanthe radially inner section 73 of the second outer ring 7. A fixed gapfor preventing interference is formed between the radially outer section41 of the first inner ring 4 and the outer peripheral surface of theradially inner section 73 of the second outer ring 7.

[0190] In the axial direction, there is a fixed gap for preventinginterference and a gap S for adjusting the pre-load between the radiallyinner section 42 of the first inner ring 4 and the radially innersection 73 of the second outer ring 7. Also, in the axial direction,there is a fixed gap for preventing interference between the radiallyinner section 42 of the first inner ring 4 and the second row of balls32. There is a fixed gap for preventing interference in the axialdirection between the intermediate section 74 of the second outer ring 7and the first row of balls 31. Furthermore, there is a fixed gap forpreventing interference in the axial direction between the radiallyouter section 41 of the first inner ring 4 and the intermediate section74 of the second outer ring 7.

[0191] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe shaft 1 side of this circular disk-shaped member 11, there is asupport member 8 that is formed such that it supports the side surfaceof the second inner ring 5. The housing 2 comprises an outer peripheralmember 21 for supporting the outer peripheral surfaces of the two outerrings 6, 7, and a side-surface member 22 for supporting the outsidesurface of the second outer ring 7.

[0192] As described above, with this double-row ball bearing, theposition of the two rows of balls 31, 32 are displaced in the radialdirection of the bearing, and by arranging the first inner ring 4 andsecond outer ring 7 such that the radially outer section 41 of the innerring 4 is located further outside in the radial direction than theradially inner section 73 of the outer ring 7, it is possible tosuppress vibration or run-out of the rotating shaft and decrease thewidth of the double-row ball bearing more than the bearing shown in FIG.14.

[0193] Moreover, with this double-row ball bearing, the radially innersection 42 of the first inner ring 4 fits around the outer peripheralsurface of the second inner ring 5, so it is possible to adjust thepre-load before installation on the shaft 1. In addition, the double-rowball bearing can be delivered already pre-loaded. Also, this double-rowball bearing can be easily installed on the shaft 1.

[0194] Furthermore, with this bearing, it is not necessary to have aring-shaped member 12, such as in the bearing showing in FIG. 10, sincethe second inner ring 5 also functions as a gap retaining member, andthus it is effective in making it possible to reduce the number ofparts.

[0195]FIG. 13 is a cross-sectional drawing showing a double-row ballbearing device of a thirteenth example of this invention.

[0196] The double-row ball bearing 3 comprises first and second innerrings 4, 5 and one outer ring 16, and is set between the shaft 1 and thehousing 2 such that it is pre-loaded by a fixed-position pre-loadingmethod.

[0197] The two rows of balls 31, 32 of the double-row ball bearing 3 arelocated such that they are displaced from each other in the radialdirection of the bearing. The ball diameter of the balls 31 of one rowis the same as that of the balls 32 of the other row. One row (firstrow) of balls 31 is located further outside in the radial direction ofthe bearing than the other row (second row) of balls 32. The differencebetween the diameter of the pitch circle of the first balls 31 and thediameter of the pitch circle of the second balls 32 is approximately 4times the diameter of the balls 31, 32. The two rows of balls 31, 32 arearranged such that distance between the centers of the balls 31, 32separated in the axial direction is equal to the radius of the balls 31,32.

[0198] The second inner ring 5 has a normal inner ring shape, however,the first inner ring 4 comprises a radially outer section 41 having araceway, and a radially inner section 42 on the shaft 1 side. The firstinner ring 4 is formed such that the width of the radially inner section42 is less than the width of the radially outer section 41, and that thedimension of the radially inner section 42 in the radial direction isgreater than that of the radially outer section 41.

[0199] Moreover, the width of the second inner ring 5 is nearly the sameas the length of the shaft 1, and the width of the radially innersection 42 of the first inner ring 4 is about ⅓ the width of the secondinner ring 5. The radially inner section 42 of the first inner ring 4fits around the outer peripheral surface of the second inner ring 5. Inother words, the second inner ring 5 also functions as a gap retainingmember.

[0200] The outer ring 16 is constructed such that the two outer ring 6,7 shown in FIG. 12 have been integrated, and comprises a radially innersection 73 having a raceway around its inner peripheral surface for thesecond row of balls 32, a radially intermediate section that is locatedat the radial position of the first row of balls 31, and a radiallyouter section 75 having a raceway around its inner surface for the firstrow of balls 31. The width of the radially outer section 75 of the outerring 16 is nearly the same as the length of the shaft 1.

[0201] The radially outer section 41 of the first inner ring 4 islocated further outside in the radial direction than the radially innersection 76 of the outer ring 16. There is a fixed gap for preventinginterference formed between the radially outer section 41 of the firstinner ring 4 and the outer peripheral surface of the radially innersection 73 of the outer ring 16.

[0202] In the axial direction, there is a fixed gap for preventinginterference and a gap S for adjusting the pre-load between the radiallyinner section 42 of the first inner ring 4 and the radially innersection 73 of the outer ring 16. Also, in the axial direction, there isa fixed gap for preventing interference between the radially innersection 42 of the first inner ring 4 and the second row of balls 32.There is a fixed gap for preventing interference in the axial directionbetween the radially intermediate section 77 of the outer ring 16 andthe first row of balls 31. Furthermore, there is a fixed gap forpreventing interference in the axial direction between the radiallyouter section 41 of the first inner ring 4 and the radially intermediatesection 77 of the outer ring 16.

[0203] On one end of the shaft 1 in the lengthwise direction, there is acircular disk-shaped member 11 that is integrated with the shaft 1. Onthe shaft 1 side of this circular disk-shaped member 11, there is asupport member 8 that is formed such that it supports the side surfaceof the second inner ring 5. The housing 2 comprises an outer peripheralmember 21 for supporting the outer peripheral surface of the outer ring16, and a side-surface member 22 for supporting the outside surface ofthe outer ring 16.

[0204] As described above, with this double-row ball bearing, theposition of the two rows of balls 31, 32 are displaced in the radialdirection of the bearing, and by placing the radially outer section 41of the first inner ring 4 further outside in the radial direction thanthe radially inner section 76 of the outer ring 16, it is possible tosuppress vibration or run-out of the rotating shaft and decrease thewidth of the double-row ball bearing more than the bearing shown in FIG.14.

[0205] Moreover, with this double-row ball bearing, the radially innersection 42 of the first inner ring 4 fits around the outer peripheralsurface of the second inner ring 5, so it is possible to adjust thepre-load before installation on the shaft 1. In addition, the double-rowball bearing can be delivered already pre-loaded. Also, this double-rowball bearing can be easily installed on the shaft 1.

[0206] Furthermore, with this bearing, it is not necessary to have aring-shaped member 12, such as in the bearing showing in FIG. 10, sincethe second inner ring 5 also functions as a gap retaining member, andthe two outer ring 6, 7 shown in FIG. 12 are integrated into one outerring 17, in which raceways for both rows of balls are formed. Thereforeit is effective in making it possible to reduce the number of partscomparing with the structure in FIG. 12.

[0207]FIG. 14 is a cross-sectional drawing showing a double-row ballbearing device of a comparative example of this invention.

[0208] The double-row ball bearing comprises first and second innerrings 4, 5 and first and second outer rings 6, 7, and it set between theshaft 1 and housing 2 such that it is pre-loaded by a fixed-positionpre-loading method.

[0209] The two inner rings 4, 5 are formed such that they have the samewidth, and that the width is fixed in the radial direction. The twoouter rings 6, 7 are formed such that they have the same width, and thatthe width is fixed in the radial direction. The two rows of balls 31, 32are formed such that the ball diameter of the balls 31 of one row is thesame as the diameter of the balls 32 of the other row, and they arearranged at the same position in the radial direction.

[0210] The first inner ring 4 and the second inner ring 5 face eachother in the axial direction with a gap S for adjusting the pre-load.The inner diameter of the first inner ring 4 is the same as that of thesecond inner ring 5, and they both fit in a ring-shaped member (gapretaining member) 12. The ring-shaped member 12 fits over the shaft 1.

[0211] In another feature of the present invention, a bearing devicecomprises a pair of outer races each having an inner peripheral surfaceon which an outer ring raceway is formed (an outer race can have a pairof outer ring raceways), a pair of inner races each having an outerperipheral surface on which an inner ring raceway is formed, a pluralityof balls rollably provided between the outer ring raceway and the innerring raceway, a retainer provided between the inner peripheral surfaceof the respective outer races and the outer peripheral surface of therespective inner races to rollably hold the balls, the pair of outerraces having axial end surfaces opposing each other, the pair of innerraces having axial end surfaces opposing each other, the pair of outerraces fitted into and fixed to an outer member with the axial endsurfaces thereof abutted to each other, and the pair of inner racesfitted into and fixed to an inner member in the state where a desiredpreload is applied to the balls by pushing the pair of inner races witha gap between the axial end surfaces thereof to come closer to eachother, wherein the axial center of the outer ring raceways is biasedtoward the side of the abutment of the outer races in the axialdirection of the outer races, and wherein the retainer is of the crowntype and comprises an annular main portion and a plurality of resilientportions provided on one axial side of the main portion such that apocket is formed between a pair of circumferentially adjacent resilientportions, and wherein the main portion is provided closer to eitheraxial end of the bearing device and wherein the outer races and innerraces have an axial end surface on either axial side of the bearingdevice, such that the axial end surfaces of the outer races and innerraces are placed at substantially the same location in the axialdirection.

[0212]FIG. 15 to FIG. 18 show a fourteenth example of the presentinvention, wherein the bearing device 101 has a pair of outer rings 110which have an inner peripheral surface on which the outer ring raceway109 is formed, and can be fitted into the outer member or hub 104, apair of inner rings 108 which have an outer peripheral surface on whichthe inner ring raceway 107 is formed, and can be fitted onto the innermember or support shaft 103, a plurality of balls rotatably providedbetween the inner ring raceways 107 and the outer ring raceways 109,respectively, and a pair of retainers 112 provided between the innerperipheral surface of the outer rings 110 and the outer peripheralsurface of the inner rings 108 to rotatably support the balls,respectively. When using the bearing device 101, the axially inner endsurfaces of the pair of the outer rings 110 are abutted to each other,and in this state, the pair of the outer rings 110 are fitted into andfixed to the hub 104 by way of interference fitting or adhesion etc.

[0213] In the present specification, the term “axially inner” means thesides in which the outer rings 110 and the inner rings 108 face eachother in the axial direction, while the term “axially outer” means thesides in which the outer rings 110 and the inner rings 108 do not faceeach other in the axial direction.

[0214] In addition, the axially inner end surfaces of the pair of theinner rings 108 are provided with a gap 116 therebetween, and in thisstate, a tool (not shown) is used in order that the pair of the innerrings 108 are pushed so as to come closer each other to apply a desiredpre-load to the balls 111, and in this state, the pair of inner rings108 are fitted onto and fixed to the support shaft 103 by way ofinterference fitting or adhesion etc.

[0215] In the case of the present example, the diameter d₁₁ (FIG. 16) ofthe balls is 0.5 mm.

[0216] In the case of the present invention, the retainers 112 are of acrown type and comprise an annular main portion 117 and a plurality ofresilient portions 118 provided on one of the axial surfaces, such thata pocket is formed between a pair of circumferentially adjacentresilient portions. In the present example, the retainers 112 are madeof a synthetic resin such as polyamide 66.

[0217] In the case of the present invention, the axial center of theouter ring raceways 109 is biased to the side of abutment between theouter rings 110 with respect to the axial direction of the outer rings110. Accordingly, provided that L₁ represents the axial length betweenthe axial center of the outer ring raceways 109 and the axially outerend surface of the outer rings 110, and that L₂ (FIG. 16) represents theaxial length between the axial center of the outer ring raceways 109 andthe axially inner end surface of the outer rings 110, L₁ is larger thanL₂ (L₁>L₂). In addition, provided that L₃ represents the axial lengthbetween the axially inner end surface of the inner rings 108 and theaxial center of the inner ring raceways 107 on the outer peripheralsurface of the inner rings 108, and L₂ represents the axial lengthbetween the axially inner end surface of the outer ring 110 around theinner ring 108 and the axial center of the outer ring raceway 109 on theinner peripheral surface of the outer rings 110, L₃ is smaller than L₂(L₃<L₂).

[0218] In the case of the present invention, the main portions 117 ofthe retainers 112 are located closer to the axial opposite ends of thebearing device 101. And, the axially outer end surface of the outerrings 110 is provided at substantially the same position as the axiallyouter end surface of the inner rings 108. The term “at substantially thesame position” means that the axial displacement is less than the sum ofthe displacement due to the predetermined pre-load on the balls 111 andthe tolerance in size required in process, and in this example, it is upto 0.25 mm.

[0219] The end surface of the main portions 117 of the retainers 112does not project in the axially outer side than the outer end surface ofthe outer and inner rings 110, 108 when the respective members arelocated at the median in the range of size tolerance, but may slightlyproject depending on the produced condition. In addition, with thepresent example, part of the balls 111 is axially slightly projected tothe side of the gap 116 than the inner end surface of the inner rings108.

[0220] With the bearing device constructed as mentioned above, apredetermined pre-load is applied to the balls 111 to sufficientlysecure the bearing rigidity, while the whole axial length can be madesufficiently small. The following are reasons for it.

[0221] First, as to the first reason, with the present invention, theaxial center of the outer ring raceways 109 is biased to the side of theabutment between the outer rings 110 with respect to the axial directionof the outer rings 110.

[0222] The axial length L₃ between the axially inner end surface of theinner rings 108 and the axial center of the inner ring raceways 107 onthe outer peripheral surface of the inner rings 108 is smaller than theaxial length L₂ between the axially inner end surface of the outer ring110 around the inner ring 108 and the axial center of the outer ringraceways 109 on the inner peripheral surface of the outer rings 110(L₃<L₂).

[0223] On the other hand, with the conventional structure as shown in JPPatent Publication Toku Kai Hei 10-159843, the axial center of the outerring raceways is biased to the side opposite to the abutment between theouter rings with respect to the axial direction of the outer rings. And,as in the bearing unit 101 shown in FIG. 19 for comparison, the axialcenter of the outer ring raceways 109 is located at the same position tothe axial center of the outer rings 110, and in this case, although thewhole length in the axial direction can be made shorter in a degreecomparing with the conventional structure, it could not be said that itis sufficiently small. Specifically, in the structure of FIG. 19, theinner end portions of the inner and outer rings 108, 110, as shown bytilted lattice hatchings, at the axially inner end portions of the innerand outer rings 108, 110 can still be cut away.

[0224] Taking these points into consideration, the axial center of theouter ring raceways 109 is axially vised to the side of the abutmentbetween the outer rings 110, and the axial length L₃ is smaller than theaxial length L₂, (L₃<L₂), as mentioned above. Consequently, the axiallength between the outer rings 110 and the axially inner end of theinner rings 108 can be made small by the amount of the axial length asillustrated by the tilted lattice hatchings in FIG. 19. Therefore, withthe present invention, the axial length of the axially inner end of theouter and inner rings 110, 108 to make the whole length of the bearingdevice 101 shorter.

[0225] Next, as to the second reason, the retainers 112 are of the crowntype and comprise an annular main portion 117 and a plurality ofresilient portions 118 provided on one axial surface of the mainportions 117, such that a pocket 119 is formed between a pair ofcircumferentially adjacent resilient portions 118. In addition, the mainportions 117 are provided closer to the axial opposite ends of thebearing device 101.

[0226] On the other hand, as in a second comparative example shown inFIG. 20, when the main portions 117 of the retainers 112 are providedcloser to the axial center of the bearing device, the whole length cannot be made sufficiently shorter. This is because the material thicknessL₁₇ of the main portions 117 in the axial direction must be made largerin a degree so as to secure the rigidity of the retainers 112. This canbe similarly true to the small sized bearing device to which the presentinvention is applied. And, as to the shoulder portions 120 a, 120 bprovided on the axially opposite sides on the outer peripheral surfaceof the inner rings 108, the necessary minimum of the minimum materialthickness of the main portions 117 is larger than the necessary minimumof the axial length L_(20b) of the shoulder portions 120 b on theradially inner side of the main portions 117.

[0227] Incidentally, the axial length of the shoulder portions 120 a,120 b is necessary to secure the strength of the shoulder portions 120a, 120 b. Accordingly, with the structure of FIG. 20, the axial lengthL₁₁ between a pair of the rows of the balls 111 is large based on theexistence of the main portions 117.

[0228] Specifically, in the structure shown in FIG. 20, a desiredpre-load is applied to the balls 111 by pushing the pair of inner rings108 such that they come closer to each other and fitted into and fixedto the support shaft 103 (FIG. 15), and in this state, based on thechange of the internal gap in the components, a load is applied to theouter rings 110 and the inner rings 108 from the balls 111 in thedirection as shown by the dotted lines α in FIG. 20.

[0229] Accordingly, with the pair of shoulder portions 120 a, 120 bprovided axially both sides of the outer peripheral surface of the innerrings 108, the shoulder portions 120 b on the axially outer side towhich the load is applied from the balls 111 is close to the operatingpoint of this load. Therefore, their strength is insufficient comparingwith the strength of the shoulder portions 120 b in the axially inside.Accordingly, the axial length L_(20a) of the shoulder portions 120 a onthe axially outside must be sufficiently large to secure the strength.

[0230] On the other hand, the shoulder portions 120 b on the axiallyinside are not subject to the load from the balls 111, and thereforethere is no particular need that the axial length L_(20b) is large.However,.even if the axial length L_(20b) of the shoulder portions 120 bis short without changing the structure of FIG. 20, the axial length L₁₁between the pair of rows of the balls 111 could not be small, and it isimpossible to make the bearing device 101 small.

[0231] On the other hand, in the present invention, the main portions117 of the retainers 112 are located closer to the both axial ends ofthe bearing device 101. Accordingly, by eliminating the main portions117 from between the pair of rows of the balls 111, the axial length L₁₁(FIG. 15) between the pair of rows of the balls can be made shorter thanthe axial length L₁₁ shown in FIG. 20.

[0232] In the present invention, the main portions 117 are locatedcloser to the both ends of the bearing device in the axial direction,and so the axial length of the axially outer portion than the balls 111is longer than the axial length of the axially inner portion.Specifically, when the main portions 117 are located closer to the bothaxial ends of the bearing device 101, the axial length (L₁₇+d₁₁/2)between the axial end surfaces of the main portions 117 and the centerof the balls 111 could not be made smaller comparing with the case wherethe main portions 117 are located closer to the axial center of thebearing device 101.

[0233] Supposed that the inner rings 108 are moved closer to each otherfor. preloading, when the main portions 117 are located closer to theboth axial ends of the bearing device 101, the size d₁₆ of the gap 116between the axial end surfaces of the inner rings 108 or retainers 112could not be made smaller comparing with the case where the mainportions 117 are located closer to the axial center of the bearingdevice 101.

[0234] On the other hand, the axial length between the axial end surfaceof the inner ring 108 on the side where the main portions 117 are notprovided, and the center of the balls 111 is changed depending on theaxial length L_(20a) (or L_(20b)) required to secure the strength of theshoulder portion 120 a (or 120 b) of the inner rings 108 located in thatportion.

[0235] When looking at the drawings taking these points intoconsideration, it is found that in the structure shown in FIG. 20, aload from the balls 111 under preload is applied to the axially outershoulder portion 120 a of the inner rings 108 on the side where the mainportions 117 are not provided. Therefore, in spite that the mainportions 117 are not provided, the axial length L_(20a) of the shoulderportion 120 a on the axially outer side must be made larger. This leadsto the increase in size of the bearing device because the axial lengthon the inner and outer sides of the balls 111 must be made larger.

[0236] On the other hand, in the present invention, a load from theballs 111 under preload is not applied to the axially inner shoulderportion 120 b of the inner rings 108 on the side where the main portions117 are not provided. Accordingly, in the present invention, it is notnecessarily taken into consideration to prevent any interference of themain portions 117, and therefore the axial length L_(20b) of theshoulder portions 120 b on the axially inner side of the inner rings 108can be made smaller than the axial length L_(20a) of the shoulderportions 120 a on the axially outer side of the inner rings 108 as shownin FIG. 20. That is L_(20b)<L_(20a).

[0237] In addition, in the present embodiment, the axially outer endsurface of the outer rings 110 is located at the substantially sameposition in the axial direction as the axially outer end surface of theinner rings 108. And, the main portions 117 are arranged around theshoulder portion 120 a having the axial size enlarged for largerstrength, and so the respective end surfaces can be located at thesubstantially same position as the axially outer end surface of theouter rings 110 and inner rings 108. As a result, in the presentembodiment, the whole axial length of the bearing device 101 can be madesmaller by the amount equal to the length twice the difference δ(=L_(20a)−L_(20b)) between the axial length L_(20b) of the shoulderportions 120 b on the axially inner side of the inner rings 108 and theshoulder portion 120 a on the axially outer side of the inner rings 108in the structure as shown in FIG. 20.

[0238] In the present embodiment, the axial length L₂₁ of the shoulderportions 121 on the axially inner side of the outer rings 110 under theload from the balls 111 due to preloading can be made smaller than theaxial length L₂₁ of the shoulder portions 121 on the axially inner sideof the outer rings 110 as shown in FIG. 20. That is L₂₁<L₁₁.

[0239] However, in the present embodiment, the inner end surfaces of theshoulder portions 121 are abutted to each other. Accordingly, the axiallength L₂₁ of the shoulder portions 121 is equal to the sum of the axiallength L_(20b) of the shoulder portions 120 b on the axially inner sideof the inner rings 108 and the a half (d₁₆/2) of the gap 116. That is,L₂₁=L_(20b)+d₁₆/2. It is securely longer than the axial length L_(20a)of the shoulder portion 120 a of the inner rings 108 shown in FIG. 20.In addition, the loads from the balls 111 to the shoulder portions 121are offset each other because they are exerted in the direction to pushthe shoulder portions 121 each other. Consequently, the strength of theshoulder portions 121 is never insufficient.

[0240] Consequently, according to the present embodiment of theinvention, the whole axial length of the bearing device can besufficiently short for miniaturizing and light weighting. Therefore,even if there are large differences in linear expansion coefficientbetween the materials for the hub 104, support shaft 103, outer rings110 and inner rings 108, and even if there are differences intemperature between the outer rings 110 and the inner rings 108 duringuse, deformation caused due to the differences in thermal expansionamount in the fitting fixing portions of the members 104, 103, 110, 108can be made small. Consequently, the amount of change in the bearingrigidity can be very small.

[0241] In the present embodiment, with the main portions 117 of theretainers 112, the minimum material thickness L₁₇ of the portioncorresponding to the pockets 119 is larger than 0.1 mm and less than 0.2mm. The control to this range of the minimum material thickness L₁₇ isto sufficiently secure the durability and to make the whole axial lengthof the bearing device sufficiently short. Specifically, if the minimummaterial thickness L₁₇ of the main portions 117 is 0.2 mm or more, it isdifficult to make the whole axial length comparing with the conventionalcompact bearing device, while if the minimum material thickness L₁₇ ofthe main portions 117 is 0.1 mm or less, it is difficult to sufficientlysecure the rigidity of the retainers 112. For example, when the minimummaterial thickness L₁₇ is 0.1 mm, and when the inner and outer rings108, 110 are relatively rotated at the speed of 5000 rpm, the retainers112 could not bear the centrifugal force thereon, and part of them couldbe deformed. Therefore, when the minimum material thickness L₁₇ is 0.1mm, the rotation speed during use must be controlled less than 5000 rpm.

[0242] Incidentally, the ratio of the minimum material thickness L₁₇ tothe diameter d₁₁ of the balls 111 is in the range of 0.2 to 0.4. Thatis, 0.2<L₁₇/d₁₁<0.4.

[0243] Moreover, in the present embodiment, part of the balls held inthe retainer 112 is slightly axially projected than the inner endsurface of the inner rings 108 toward the gap 116. Therefore, the axiallength L₄ between the balls 111 can be small, and so the whole axiallength of the bearing device 101 can be further small.

[0244] Incidentally generally speaking, in the bearing device where apair of ball bearings are combined with each other and the balls of thebearings are preloaded for use, the load applied to the outer rings andto the inner rings from the balls is tilted indirection with referenceto the central axis of the bearing device. Accordingly, a pair ofshoulder portions are provided on the axially opposite sides of theinner peripheral surface of the outer ring and of the outer peripheralsurface of the inner ring, such that they are different from each otherin diameter. And, even if the balls are pushed to one of the shoulderportions, the balls are prevented from riding on the shoulder portion.

[0245] On the other hand, in the present embodiment, a pair of theshoulder portions 120 a, 120 b, 121, 122 are provided on the axiallyopposite sides of the inner peripheral surface of the outer rings 110and of the outer peripheral surface of the inner rings 108, such thatthey have substantially the same diameter. This is because the presentembodiment is applied to the extremely small bearing device being e.g. 2mm in inner diameter and 9 mm in outer diameter, where the process formanufacturing the bearing device is difficult if the shoulder portions120 a, 120 b, 121, 122 are different from each other in diameter. Withthe extremely small bearing device 101, since the load based on thepreload on the balls 111 is comparatively small, the balls 111 neverride on the shoulder portions 120 a, 121 on the preload side even if theshoulder portions 120 a, 120 b, 121, 122 in the outer and inner rings110, 108 have the same diameter.

[0246] In the present embodiment, the ratio of the diameter d₁₁ of theballs 111 to the axial length L₈ of the inner rings 108 is 0.71 and theratio of the diameter d₁₁ of the balls 111 to the axial length L₁₀ ofthe outer rings 110 is 0.65. Therefore, d₁₁/L₈≧0.6, and d₁₁/L₁₀ ≧0.6.This is substantially larger than in the case of the conventionalbearing device where the crown type retainer is installed with the ballshaving a diameter up to 0.5 mm. This is because, in the presentembodiment, the whole axial length of the bearing device 101 can besufficiently small even when the diameter d₁₁ of the balls 111 is set ata fixed value.

[0247] With the present embodiment, the bearing device can beminiaturized and lightweighted while securing sufficient bearingrigidity under preload. For example, the main portions 117 of theretainers 112 are made to have a minimum material thickness L₁₇ as smallas possible while keeping the durability of the retainers 112, and sothe axial length of the bearing device 101 can be small, specifically1.6 mm or less.

[0248] Incidentally, when implementing this embodiment, the outer ringis not necessarily divided in two pieces. A single piece of outer ringhaving a double row of outer ring raceways on its inner peripheralsurface can be used so long as inconvenience more or less caused inmanufacturing and assembling is accepted.

[0249] In another feature of the present invention, a bearing devicecomprises a pair of outer races each having an inner peripheral surfaceon which an outer ring raceway is formed (an outer ring can have tworaceways), a pair of inner races each having an outer peripheral surfaceon which an inner ring raceway is formed, a plurality of balls rotatablyprovided between the outer ring raceway and the inner ring raceway, acylindrical sleeve provided on the radially inside of the pair of innerrings, the pair of outer races having an axial end surface,respectively, such that the axial end surfaces are opposed to eachother, the pair of inner races having an axial end surface,respectively, such that the axial end surfaces are opposed to eachother, the axial end surfaces of the outer races abutted to each other,the pair of inner races fitted onto and fixed to the sleeve in the statewhere a desired preload is applied to the balls by pushing the pair ofinner races with a gap between the axial end surfaces thereof to comecloser to each other.

[0250]FIG. 21 shows a fifteenth example of the embodiment of the presentinvention, wherein the bearing device 101 has a pair of outer rings 110which have an inner peripheral surface on which the outer ring raceway109 is formed, and can be fitted into the outer member or hub 104 withinterference fit or adhesion, a pair of inner rings 108 which have anouter peripheral surface on which the inner ring raceway 107 is formed,a plurality of balls 111 rotatably provided between the inner ringraceways 107 and the outer ring raceways 109, respectively, and acylindrical sleeve 212 fitted onto and fixed by the inner member orsupport shaft (not shown) by way of interference fit with a slightinterference. FIGS. 17 and 18 can be referred to for reference in thisexample which has a similar structure. The inner and outer peripheralsurfaces of the sleeve 212 are formed in a simple cylindrical shape.And, the axial length L₈ of the inner rings 108 is smaller than theaxial length L₁₀ of the outer rings 110. That is, L₈<L₁₀.

[0251] The axial center of the outer ring raceways 109 and the innerring raceways 107 are provided at the central location in the axialdirection of the outer rings 110 and inner rings 108. Specifically, theaxial length L₁ between the axial center of the outer ring raceways 109and the axially outer end surface of the outer rings 110 is the same tothe axial length L₂ between the axial center of the outer ring raceways109 and the axially inner end surface of the outer rings 110. That is,L₁=L₂. And, the axial length L₃ between the axial center of the innerring raceways 107 and the axially outer end surface of the inner rings108 is the same to the axial length L₄ between the axial center of theinner ring raceways 107 and the axially inner end surface of the innerrings 108. That is, L₃=L₄.

[0252] Accordingly, the axial length L₄ between the axial center of theinner ring raceways 107 and the axially inner end surface of the innerrings 108 is smaller than the axial length L₂ between the axial centerof the outer ring raceways 109 and the axially inner end surface of theouter rings 110. That is, L₄<L₂. And, the axial length L₁₂ of the sleeve212 is about twice the axial length L₁₀ of the pair of outer rings 110.That is, L₁₂≈2L₁₀.

[0253] A pair of retainers 112 are provided between the inner peripheralsurface of the outer rings 110 and the outer peripheral surface of theinner rings 108 to rotatably hold the balls 111. The retainers 112 is ofthe crown type and are made of a synthetic resin such as polyamide 66and formed as in the fourteenth example. The main portions 117 arelocated closer to the axially opposite ends of the bearing device. And,seal rings 217 are provided between the inner peripheral surface of theouter end of the outer rings 110 and the outer peripheral surface of theouter end of the inner rings 108 to block the both axial ends of thespace where the balls 111 are arranged.

[0254] The axially opposite inner end surfaces of the pair of outerrings 110 are abutted to each other, and in this state, the pair ofinner rings 108 are pushed to come close to each other while a gap 116exists between the axial inner end surfaces, whereby the inner rings 108are fitted onto and fixed to the sleeve 212 by way of interference fitor adhesion with the balls 111 under the desired preload.

[0255] The inner rings 108 are fitted onto the sleeve 212 for fixing bythe bearing device manufacturer using a special apparatus, as for theconventional structures, which includes a measurement device for naturalfrequency and a device for ultraviolet ray radiation.

[0256] In the state where the inner rings 108 are fitted onto the sleeve212 for fixing, the axially outer end surface of the outer rings 110, atthe location of the axially opposite ends of the bearing device, isprovided at substantially the same position as the axially outer endsurface of the sleeve 212.

[0257] The term “at substantially the same position” means that theaxial displacement is less than the tolerance in size required forprocessing.

[0258] The bearing device 101 of the present embodiment of the inventioncan be easily installed on the support shaft 3 at a manufacturer havingno special apparatus to apply a desired preload. Specifically, thebearing device 101 of the present embodiment of the invention can beprovided with a desired preload at a bearing manufacturer having aspecial apparatus. In this state, the support shaft 3 having variousparts around it is not mounted to the bearing device 101. And, thebearing device 101 is sent from the bearing manufacturer to amanufacturer of article in order that the bearing device 101 isinstalled in the article. At this manufacturer of article, the sleeve212 of the bearing device 101 is fitted for fixing to the support shaft103 by way of interference fit with slight interference. The process ofsuch fitting can be made without a special apparatus for preloading.Accordingly, the bearing device 101 of the present invention can beeasily mounted to the support shaft 103 by the article manufacturerhaving no special apparatus for preloading. Consequently, with thepresent invention, the operation of transporting for manufacturing thearticle with the bearing device therein can be lightened, and the costof the article having the bearing device 101 therein can be decreased.In addition, the same bearing device 101 can be mounted to variousapparatus, and therefore mass production for the bearing device ispossible, which leads to the cost reduction of the bearing device 101.

[0259] Incidentally, when the sleeve 212 is fitted onto the supportshaft 103 for fixing at the article manufacturer, the interference ofthe sleeve with respect to the support shaft 103 is slight in order notto change the desired preload previously applied to the bearing device101.

[0260] In the present example, the axial center of the inner ringraceways 107 and the axial center of the outer ring raceways 109 arelocated at the center in the axial direction of the inner and outerrings 108, 110. Accordingly, in the present example, when the inner andouter rings 108, 110 are set to the processing apparatus where the innerring raceways 107 and the outer ring raceways 109 etc. are subjected tothe polishing or super finishing after the inner rings 108 and outerrings 110 are subjected to heat treatment, the inconvenient step tocontrol the direction of the inner rings 108 or outer rings 110 foradjustment in location of the inner ring raceways 107 and outer ringraceways 109 can be removed.

[0261] In the case of the present invention, the sleeve 212 is fittedfor fixing to the support shaft 103 with slight interference, but it ispossible to fix the sleeve 212 to the support shaft 103 by way ofclearance fitting and adhesive on the support shaft 103.

[0262] It is desirable that when the sleeve 212 is fixed with adhesiveto the support shaft 103, the sleeve 212 and the support shaft 103 arekept in a horizontal attitude and under the pushing force forpreloading, so that the adhesive is naturally solidified. This isbecause if the sleeve 212 is fixed to the support shaft 103 by keepingthe state where the sleeve 212 and support shaft 103 are arranged suchthat they are tilted with reference to the vertical direction orhorizontal direction, until the adhesive is naturally solidified, anyinconvenient process would be required to temporality fix the sleeve 212with a tool to the support shaft 103 so as to prevent the sleeve 212from moving in the direction so that sleeve 21 comes off from thesupport shaft 103. When the adhesive is naturally solidified, anyspecial device for ultraviolet ray radiation for instant solidificationis not need for use.

[0263] Incidentally, in the example illustrated, the axial outer endsurface of the outer rings 110 is located substantially at the sameaxial direction to the axial end surface of the sleeve 212. On the otherhand, if the axial end surface of the sleeve 212 is located at alocation slightly inset from the axial outer end surface of the outerrings 110, the possibility of troubles such that the end surface of thesleeve 212 is bumped during transportation of the bearing device 101 tochange the set preload load would be decreased.

[0264]FIG. 22 shows a sixteenth example of the embodiment of the presentinvention, where the outer rings 110 are located closer to the axialopposite ends of the bearing device 101, and the axial length of theaxially outer end of the outer rings 110 and of both axial ends of thesleeve 212 is shorter than the case of the fifteenth example. Therefore,in this embodiment, the length L₁ between the axial center of the outerring raceways 109 and the axially outer end surface of the outer rings110 is shorter than the axial length L₂ between the axial center of theouter ring raceways 109 and the axially inner end surface of the outerrings 110. That is, L₁<L₂.

[0265] Specifically, the axial center of the outer ring raceways 109 isbiased to the side opposite to the abutment of the outer rings 110. And,the outside end surface of the outer rings 110, the outside end surfaceof the inner rings 108 and the end surfaces of the sleeve are placedsubstantially at the same location in the axial direction.

[0266] Incidentally, the term “substantially at the same location” meansthat it is not axially displaced more than the sum of the displacementcaused by applying the predetermined preload to the balls 111 and thetolerance in dimension required for processing, and that it is 0.25 mmor less in the present example. With 0.25 mm or less, they are deemed tobe substantially at the same location.

[0267] The whole axial length of the bearing device 101 can be shorterin the present example than in the fifteenth example. Accordingly, thebearing device 101 in the present example can be set in a space smallerthan in the fifteenth example.

[0268] Incidentally, in the present example, the outer end surface ofthe inner rings 108 is placed substantially at the same position in theaxial direction to the end surface of the sleeve 212. Accordingly, whenthe sleeve 212 is fitted onto the support shaft 103 for fixing withinterference, the outer diameter of the pressing device is made smallerthan the inner diameter of the inner rings 108, so that the inner rings108 and the sleeve 212 are not relatively displaced in the axialdirection during pressing, and that the previously set preload is notchanged.

[0269] The other portions of the structure and operation are the same tothose of the fifteenth example.

[0270]FIGS. 23 and 24 show a seventeenth example of the embodiment ofthe present invention. In the case of the present invention, the axialcenter of the outer ring raceways 109 is biased to the abutment sidebetween the outer rings 110 with respect to the axial direction of theouter rings 110. Accordingly, provided that L₁ represents the axiallength between the axial center of the outer ring raceways 109 and theaxially outer end surface of the outer rings 110, and that L₂ representsthe axial length between the axial center of the outer ring raceways 109and the axially inner end surface of the outer rings 110, L₁ is largerthan L₂(L₁>L₂).

[0271] In the present example, different from the previous examples, theseal ring 217 of FIG. 21 is not provided the inner peripheral surface ofthe outer end of the outer rings 110 and the outer peripheral surface ofthe outer end of the inner rings 108. In addition, the main portions 117of the retainers 112 are arranged closer to the both axial ends of thebearing device 101. And, the outer end surface of the outer rings 110,the outer end surface of the inner rings 108, and the end surfaces ofthe sleeve 212 are placed substantially at the same location in theaxial direction as previously mentioned. In the present example, it is0.25 mm or less. In addition, the end surface of the main portions 117of the retainers 112 does not project in the axially outer directionthan the axially outer end surfaces of the outer and inner rings 110 and108 with respect to the median of the size tolerance range of thecomponent members. However, the end surface of the main portions 114 mayslightly project, depending on the produced condition, than the axiallyouter end surfaces of the outer and inner rings 110 and 108. Inaddition, with the present example, part of the balls 111 is axiallyslightly projected to the side of the gap 116 than the axially inner endsurface of the inner rings 108.

[0272] The whole axial length of the bearing device 101 in the presentexample can be further shorter than in the fifteenth example. This isbecause, in the present example, the axial center of the outer ringraceways 109 is biased to the abutment side between the outer rings 110with respect to the axial direction of the outer rings 110. Accordingly,the axial length of the shoulder portion 119 on the axially inner sideof the inner peripheral surface of the outer rings 110 and of theshoulder portion 120 on the axially inner side of the outer peripheralsurface of the inner rings 108 can be made shorter than in the previousexamples. In addition, part of the balls 111 kept in the retainers 112are slightly projected from the inner end surface of the inner rings 108toward the side where the gap exists. Accordingly, the axial length L₅of the space between the rows of balls 111 in the present invention canbe made shorter than in the previous examples.

[0273] In the present invention, no seal ring is not provided betweenthe inner peripheral surface of the axially outer end of the outer rings110 and the outer peripheral surface of the axially outer end of theinner rings 108. Accordingly, the axial length of the axially outerportion than the balls 111 and of the bearing device 101 in the presentinvention can be made shorter than in the fifteenth example of FIG. 22.Therefore, the bearing device of the present example can be set in thespace which is further smaller than in the case of the fifteenthexample.

[0274] In the present example, the main portions 117 of the retainers112 are located closer to the both axial ends of the bearing device 101,which also leads to the reduction in the whole length of the bearingdevice 101. Specifically, the minimum material thickness L₁₄ of the mainportions 117 in the axial direction must be large in a degree to securethe rigidity of the retainers 112. Accordingly, in the present examplewhere the main portions 117 are arranged closer to the both axial endsof the bearing device 101, comparing with the case where the mainportions 117 are arrange at the axial center of the bearing device 101,it is impossible to make smaller the axial length (L₁₄+d₁₁/2) betweenthe axial end surface and the center of the balls 111 which isdetermined by the minimum material thickness (L₁₄) of the main portions117 and the diameter (d₁₁) of the balls 111.

[0275] However, the shoulder portions 120 a, 120 b are different fromeach other in the required minimum axial length on the both axial endsof the inner rings 108. Specifically, by pushing the inner rings 108 tocome closer each other to apply the desired preload to the balls 111,the load is applied to the outer and inner rings 110, 108 from the balls111 as directed in the direction shown by the dotted lines α in FIG. 20based on the change in the internal gaps in the component members in thebearing device 101. Therefore, with the pair of shoulder portions 120 a,120 b provided on both axial ends of the outer peripheral surface of theinner rings 108, the axially outer shoulder portions 120 b, closer tothe action point of the load, must have a strength larger than that ofthe axially inner shoulder portions 120 a. The axially outer shoulderportions 120 b must be axially longer than the axially inner shoulderportions 120 a. Consequently, the axial length of the axially innershoulder portions 120 a can be made sufficiently shorter if the mainportions 117 of the retainers 112 do not exist around the axially innershoulder portions 120 a. On the other hand, even if the main portions117 of the retainers 112 do not exist around the axially outer shoulderportions 120 b, the axial length of the axially outer shoulder portions120 b could not be made shorter than the length of the axially innershoulder portions 120 a.

[0276] Accordingly, in the present example, the main portions 117 of theretainers 112 are arranged closer to both axial ends of the bearingdevice 101 around the axially outer shoulder portions 120 b of the innerrings 108 to which the load is applied based on the preload. Therefore,in the present embodiment, the axial length of the axially innershoulder portions 120 a of the inner rings 108 to which the load is notapplied, can be made sufficiently shorter without being interfered bythe existence of the main portions 117. Consequently, the whole axiallength of the bearing device can be made smaller than that of theprevious examples.

[0277] In the present example, the axial length of the axially innershoulder portions 219 of the outer rings 110 to which the load isapplied from the balls 111 based on the preload, is short. However, inthe present example, the inner end surfaces of the shoulder portions 219are abutted to each other, the loads applied from the balls 111 to theshoulder portions 219 are directed to push the shoulder portions 219 toeach other and offset. In addition, since there is a gap 118 between theinner end surfaces of the inner rings 108, the axial length of theaxially inner shoulder portions 219 of the outer rings 110 is equal tothe amount of the sum of the axial length of the axially inner shoulderportions 120 a of the inner rings 108 and a half of the gap 116, andsufficiently large. Accordingly, the strength of the shoulder portions219 is never insufficient.

[0278] In the present example, since the whole axial length of thebearing device 101 can be sufficiently small, even if the materials forthe hub, the outer rings, the sleeve and the inner rings are largelydifferent in liner expansion coefficient, or even if the outer rings andinner rings are used in the different temperatures, deformation in thefitting fixing portions of these component members due to the differencein the thermal expansion can be kept small; Therefore, the change in thebearing rigidity during use can be kept extremely small.

[0279] Incidentally, when implementing this embodiment, the outer ringis not necessarily divided in two pieces. A single piece of outer ringhaving a double row of outer ring raceways on its inner peripheralsurface can be used so long as inconvenience more or less caused inmanufacturing and assembling is accepted.

[0280] In another feature of the present invention, a bearing devicecomprises a first and second outer races each having an inner peripheralsurface on which an outer ring raceway is formed, a first and secondinner races each having an outer peripheral surface on which an innerring raceway is formed, a plurality of balls rotatably provided betweenthe outer ring raceway and the inner ring raceway, the first and secondouter races having an axial end surface, respectively, such that theaxial end surfaces are opposed to each other, the first and second innerraces having first and second axial end surfaces, respectively, suchthat the first axial end surfaces are opposed to each other, and thefirst and second outer races fitted into and fixed to an outer memberwith the first axial end surfaces abutted to each other, and the firstand second inner races fitted into and fixed to an inner member in thestate where a desired preload is applied to the balls by pushing thepair of inner races with a gap between the first axial end surfacesthereof to come closer to each other, the inner member having an outerperipheral surface on part of which an outward flange is formed, theoutward flange having an axial side surface to which the second axialend surface of the first inner race is abutted for use, wherein theaxial length of the inner peripheral surface of the second inner race islarger than the axial length of the inner peripheral surface of thefirst inner race.

[0281]FIG. 25 is an eighteen example of the embodiment of the presentinvention. The present example is characterized by a structure which isvery small in the whole length in the axial direction, wherein thedimensions of the axial length of the inner peripheral surface of firstinner ring 306 a and second inner ring 306 b of the pair of the ballbearings 314 a, 314 b in order to maintain the desired performance for along period of time. The other portions of the structure and functionsare substantially the same to those of the conventional constructionwherein a pair of ball bearings with the same dimension are used and theradially inner ball bearing is supported by the central shaft. Thefeatures of the present invention and the portions different from theconventional construction are described hereinafter.

[0282] In the case of the bearing device 101 of the present embodiment,the first and second inner rings 306 a, 306 b of the pair of ballbearings 314 a, 314 b are fitted onto and fixed with adhesion on theouter peripheral surface of the inner member 303 at two locationsseparated from the outward flange portion 310. With the pair of innerrings 306 a, 306 b, one end surface of the inner ring 306 a in the axialdirection (left end surface in FIG. 25) is abutted to one surface in theaxial direction of the outward flange portion 310 (right side face inFIG. 25). And, a gap 312 is provided between the opposing end surfacesin the axial direction of the pair of the inner rings 306 a, 306 b. Theouter rings 308 of the pair of ball bearings 304 a, 304 b are the sameto each other in the axial length. With the axially opposing endsurfaces of the outer rings 308 abutted to each other, the outer rings308 are fitted into and fixed with adhesion to the outer member,specifically the housing (not shown).

[0283] Particularly, with the bearing device 101 of the presentinvention, the axial length L_(6a) of the outer peripheral surface ofthe inner ring 306 a is the same to the axial length L_(6b) of the outerperipheral surface of the inner ring 306 b. That is, L_(6a)=L_(6b). Inaddition, a circular recess portion 313 is provided at the center of theaxial end surface (right end surface in FIG. 25) of the inner ring 306 aon the side opposing the inner ring 306 b. The axial length L_(6a), ofthe inner peripheral surface of the inner ring 306 a is smaller than theaxial length L_(6a) of the outer peripheral surface of the inner ring306 a. That is, L_(6a)<L_(6a).

[0284] On the other hand, with the inner ring 306 b, a circular landportion 314 is provided at the center of the axial end surface (left endsurface in FIG. 25) of the inner ring 306 b on the side opposing theinner ring 306 a. The axial length L_(6b) of the inner peripheralsurface of the inner ring 306 b is larger than the axial length L_(6b)of the outer peripheral surface of the inner ring 306 b. That is,L_(6b),>L_(6b). Consequently, The axial length L_(6b), of the innerperipheral surface of the inner ring 306 b is larger than the axiallength L_(6a), of the inner peripheral surface of the inner ring 306 a.That is, L₆₁,<L_(6b). In addition, part of the land portion 314 on theone end surface in the axial direction of the inner ring 306 b islocated within the recess portion 317 on the axially opposite endsurface of the inner ring 306 a.

[0285] When the inner rings 306 a, 306 b are fixed with adhesion to theouter peripheral surface of the inner member 303, the factors tostrongly affect the adhesion force (bonding strength) to bond therespective inner rings 306 a, 306 b to the inner member 303 are asfollows;

[0286] 1. kinds of the adhesive,

[0287] 2. any oil exists or not on the surface on which the adhesive iscoated,

[0288] 3. the thickness of the adhesion gap and the existence or not ofthe adhesive reservoir,

[0289] 4. the area of the portion to be bonded with the adhesive(adhesion portion).

[0290] Accordingly, to make the bonding strength larger, the optimum onemust be selected from the factors 1 to 4 above.

[0291] When the present invention is implemented, adhesives of theultraviolet curable type, not being anaerobic, and epoxy resin of theheat curable type and one-part type are desirably used. Or, acrylicresin adhesive of the anaerobic and heat plastic type (Trade name:Rocktite etc.) can also used.

[0292] In the construction according to the present invention, with thefilm of the adhesive existing between the inner peripheral surface ofthe respective inner rings 306 a, 306 b and the outer peripheral surfaceof the inner member 303, at least one end surface in the axial directionis not covered by metal etc. but exposed to the ambient air.Accordingly, the anaerobic acrylic resin adhesive, when used in thiscondition, is hard to be solidified. Accordingly, when the presentinvention is implemented, it is desirable to use the ultraviolet curabletype or the epoxy resin adhesive which is not anaerobic.

[0293] As to the item 2 above, it is desirable for larger bondingstrength to sufficiently remove oil from the surface to be coated withthe adhesive. Accordingly, when implementing the present invention,organic solvent such as alcohol or xylene is used to wipe the oil fromthe inner peripheral surface of the first inner ring 306 a and secondinner ring 306 b and from the portion of the inner member 303 on whichthe respective inner rings 306 a, 306 b are fitted.

[0294] With the item 3, when implementing the present invention, theadhesion gap between the inner peripheral surface of the respectiveinner rings 306 a, 306 b and the outer peripheral surface of the innermember 303 has a thickness desirably controlled to be more than zero andup to 15 μm, and more desirably controlled to be more than zero and upto 12 μm. Specifically, as the thickness of the adhesion gap is larger,the thickness of the film of the adhesive within the adhesion gap islarger. Accordingly, it is desirable to make the adhesion gap as largeas possible so as to improve the bonding strength of the adhesive.However, when the thickness of the adhesion gap is larger than 12 μm(even the largest, 15 μm), there could be some problems, for example thefirst inner ring 306 a and second inner ring 306 b could be eccentricwith respect to the inner member 303. Therefore, the upper limit of theadhesion gap is set to be desirable 15 μm, and more desirably 12 μm.

[0295] In the case of the present invention, it is desirable that anyknurling groove such as in a tilted lattice shape or spline type can beformed on the outer peripheral surface of the inner member 303, or thatany recess groove is formed to have a width smaller than the axiallength of the respective inner rings 306 a, 306 b. Within the knurlinggroove or recess groove, part of the adhesive enters in it to increasethe amount of the adhesive, so that the bonding strength can beincreased without having the respective inner rings 306 a, 306 beccentric with respect to the inner member 303.

[0296] With the bearing device of the present invention constructed asmentioned above, the axial length L_(6a), of the inner peripheralsurface of the first inner ring 306 a on the same side as the outwardflange portion 310 is smaller, and by that amount, the axial lengthL_(6b), of the inner peripheral surface of the second inner ring 306 bon the side opposite to the outward flange portion 310 can be larger.Accordingly, when the whole axial length of the bearing device 101 isvery small while the second inner ring 306 b is fixed to the innermember with adhesion, the bonding strength between the second inner ring306 b and the inner member 303 can be sufficiently secured for a longtime of period. Specifically, although the bonding strength is stronglyaffected by the factors 1 to 4 as mentioned above, if the effects of thefactors 1 to 3 are the same, as the area of bonding portion in thefactor 4 is larger, the bonding strength is larger. With the presentinvention, the axial length L_(6b), of the inner peripheral surface ofthe second inner ring 306 b is made larger, and by that amount, thebonding area between the inner peripheral surface of the second innerring 306 b and the outer peripheral surface of the inner member 303 canbe sufficiently larger to sufficiently secure bonding strength.

[0297] With the present embodiment, the axial length L_(6a), of theinner peripheral surface of the first inner ring 306 a is small, but theaxial end surface of the first inner ring 306 a is abutted to the oneend surface in the axial direction of the outward flange portion 310,and a load based on the preload is applied to push the first inner ring306 a to the outward flange portion 310. Accordingly, even if thebonding strength between the first inner ring 306 a and the inner member303 is insufficient to support the axial load corresponding to thepreload, the first inner ring 306 a would not be displaced with respectto the inner member 303. Consequently, in the structure where the wholeaxial length is very short, the inner rings 306 a, 306 b are preventedfrom being displaced with respect to the inner member 303, so that thedesired performance can be kept for a long period of time.

[0298]FIG. 26 shows a nineteenth example of the embodiment of thepresent invention. This is different from the eighteenth example in thatwith the axial opposite end surfaces of the respective inner rings 306a, 306 b, the opposing axial end surfaces are a simple flat surface,without having the recess portion 313 and the land portion 314 (FIG.25). Particularly, the shoulder portions 315 a, 315 b are provided onthe side facing the pair of inner rings 306 a, 306 b, such that theaxial length L_(15a) is different from the axial length L_(15b).

[0299] With the pair of the inner rings 306 a, 306 b, the axial lengthL_(15a) of the shoulder portion 315 a of the second inner ring 306 b(right one in FIG. 26) on one side in the axial direction (left side inFIG. 26) is larger than the axial length L₁₆ of the shoulder portion 316of the outer ring 308 on one side in the axial direction (left side inFIG. 26) around the second inner ring 306 b. That is, L_(15a)>L₁₆.

[0300] On the other hand, the axial length L_(15b) of the shoulderportion 315 b of the first inner ring 306 a on one side in the axialdirection (right side in FIG. 26) is sufficiently smaller than the axiallength L₁₆ of the shoulder portion 316 of the outer ring 308 on one sidein the axial direction (right side in FIG. 26) provided around the firstinner ring 306 a. That is, L_(15b)<L₁₆.

[0301] And, the whole axial length of the second inner ring 306 b islarger than the whole axial length of the first inner ring 306 a.Accordingly, as in the eighteenth example, the axial length L_(6b), ofthe inner peripheral surface of the second inner ring 306 b is largerthan the axial length L_(6a), of the inner peripheral surface of thefirst inner ring 306 a.

[0302] The other portions of the structure and function aresubstantially the same to those of the eighteenth example.

[0303]FIG. 27 shows a twentieth example of the embodiment of the presentinvention, wherein the pair of first and second ball bearings 304 a, 304b are different from each other, specifically in the outer diameter ofthe respective inner rings 306 a, 306 b and in the inner diameter of therespective outer rings 308 a, 308 b. Specifically, the outer diameter ofthe inner ring 306 a of the first ball bearing 304 a (left one in Fig,27) is larger than the outer diameter of the inner ring 306 b of thesecond ball bearing 304 b (right one in FIG. 27). In addition, the innerdiameter of the outer ring 308 a of the first ball bearing 304 a issmaller than the inner diameter of the outer ring 308 b of the secondball bearing 304 b.

[0304] In addition, the axial length of the outer ring 308 b of thesecond ball bearing 304 b is larger than the axial length of the outerring 308 a of the first ball bearing 304 a. And, the axial length of theinner ring 306 b of the second ball bearing 304 b is larger than theaxial length of the inner ring 306 a of the first ball bearing 304 a.Further, with respect to the balls 309 a, 309 b of the ball bearings 304a, 304 b the outer diameter of in the first ball bearing 304 a issmaller than that in the second ball bearing 304 b.

[0305] The other portions in the structure and function aresubstantially the same to those in the nineteenth example in FIG. 26.

[0306] The examples mentioned above are directed to the structure wherethe first inner ring 306 a is abutted to the outward flange 310, andfitted onto and fixed through bonding to the inner member 303.

[0307] However, the present invention is not limited to the structure,and can be applied to the structure where the first inner ring 306 a isfitted onto and fixed to the inner member 303 with a predeterminedinterference.

What is claimed is:
 1. A bearing device comprising a shaft, a housing, adouble row of ball bearings provided between the shaft and the housingand preloaded by a fixed-position preloading method, the double row ofball bearings having a row of balls, respectively, the balls in one ofthe rows displaced from the balls in the other row in the radialdirection of the ball bearings, the double row of ball bearings having afirst and second inner races and a first and second outer races, thefirst inner race having a radially inner section on the side of theshaft and a radially outer section with a raceway, such that the widthof the radially inner section is smaller than the width of the radiallyouter section, and the second outer race having a radially outer sectionon the side of the housing and a radially inner section with a raceway,such that the width of the radially outer section is smaller than thewidth of the radially inner section, and wherein the radially outersection of the first inner race is located radially outside the radiallyinner section of the second outer race.
 2. A bearing device of claim 1,wherein the rows of the balls are spaced from each other by a distancein the axial direction between the centers of the balls, such that thedistance in the axial direction is up to the diameter of the balls, andwherein the rows of balls have a pitch circle, such that the differencein diameter between the pitch circle of one of the rows of balls and thepitch circle of the other row of balls is at least twice the diameter ofthe balls.
 3. A bearing device of one of claims 1 and 2, wherein thewidth of the first inner race is larger than the width of the secondinner race, such that the radially inner section of the first inner raceis pressed on the radially outer section of the second inner race.
 4. Abearing device comprising a pair of outer races each having an innerperipheral surface on which an outer ring raceway is formed, a pair ofinner races each having an outer peripheral surface on which an innerring raceway is formed, a plurality of balls rotatably provided betweenthe outer ring raceway and the inner ring raceway, a retainer providedbetween the inner peripheral surface of the respective outer races andthe outer peripheral surface of the respective inner races to rotatablyhold the balls, the pair of outer races having axial end surfacesopposing each other, the pair of inner races having axial end surfacesopposing each other, the pair of outer races fitted into and fixed to anouter member with the axial end surfaces thereof abutted to each other,and the pair of inner races fitted into and fixed to an inner member inthe state where a desired preload is applied to the balls by pushing thepair of inner races with a gap between the axial end surfaces thereof tocome closer to each other, wherein the axial center of the outer ringraceways is biased toward the side of the abutment of the outer races inthe axial direction of the outer races, and wherein the retainer is ofthe crown type and comprises an annular main portion and a plurality ofresilient portions provided on one axial side of the main portion suchthat a pocket is formed between a pair of circumferentially adjacentresilient portions, and wherein the main portion is provided closer toeither axial end of the bearing device and wherein the outer races andinner races have an axial end surface on either axial side of thebearing device, such that the axial end surfaces of the outer races andinner races are placed at substantially the same location in the axialdirection.
 5. A bearing device comprising an outer race having an innerperipheral surface on which a pair of outer ring raceways are formed, apair of inner races each having an outer peripheral surface on which aninner ring raceway is formed, a plurality of balls rotatably providedbetween the outer ring raceways and the inner ring raceways, a pair ofretainers provided between the inner peripheral surface of the outerrace and the outer peripheral surface of the inner races to rotatablyhold the balls, the pair of inner races having axial end surfacesopposing each other, the outer race fitted into and fixed to an outermember, the pair of inner races fitted into and fixed to an inner memberin the state where a desired preload is applied to the balls by pushingthe pair of inner races with a gap between the axial end surfacesthereof to come closer to each other, wherein the axial center of theouter ring raceways is biased toward the center of the outer race in theaxial direction of the outer race, and wherein the retainers are of thecrown type and comprise an annular main portion and a plurality ofresilient portions provided on one axial side of the main portion suchthat a pocket is formed between a pair of circumferentially adjacentresilient portions, and wherein the main portion is provided closer toeither axial end of the bearing device and wherein the outer race andinner races have an axial end surface on either axial side of thebearing device, such that the axial end surfaces of the outer race andinner races are placed at substantially same location in the axialdirection.
 6. A bearing device comprising a pair of outer races eachhaving an inner peripheral surface on which an outer ring raceway isformed, a pair of inner races each having an outer peripheral surface onwhich an inner ring raceway is formed, a plurality of balls rotatablyprovided between the outer ring raceway and the inner ring raceway, acylindrical sleeve provided on the radially inside of the pair of innerrings, the pair of outer races having an axial end surface,respectively, such that the axial end surfaces are opposed to eachother, the pair of inner races having an axial end surface,respectively, such that axial end surfaces are opposed to each other,the axial end surfaces of the outer races abutted to each other, thepair of inner races fitted onto and fixed to the sleeve in the statewhere a desired preload is applied to the balls by pushing the pair ofinner races with a gap between the axial end surfaces thereof to comecloser to each other.
 7. A bearing device comprising an outer racehaving an inner peripheral surface on which a pair of outer ringraceways are formed, a pair of inner races each having an outerperipheral surface on which an inner ring raceway is formed, a pluralityof balls rotatably provided between the outer ring raceways and theinner ring raceways, a cylindrical sleeve provided on the radiallyinside of the pair of inner rings, the pair of inner races having anaxial end surface, respectively, such that the axial end surfaces areopposed to each other, and the pair of inner races being fitted onto andfixed by the sleeve in the state where a desired preload is applied tothe balls by pushing the inner races with a gap between the axial endsurfaces thereof to come closer to each other.
 8. A bearing devicecomprising a first and second outer races each having an innerperipheral surface on which an outer ring raceway is formed, a first andsecond inner races each having an outer peripheral surface on which aninner ring raceway is formed, a plurality of balls rotatably providedbetween the outer ring raceway and the inner ring raceway, the first andsecond outer races having an axial end surface, respectively, such thatthe axial end surfaces are opposed to each other, the first and secondinner races having first and second axial end surfaces, respectively,such that the first axial end surfaces are opposed to each other, andthe first and second outer races fitted into and fixed to an outermember with the first axial end surfaces abutted to each other, and thefirst and second inner races fitted into and fixed to an inner member inthe state where a desired preload is applied to the balls by pushing thepair of inner races with a gap between the first axial end surfacesthereof to come closer to each other, the inner member having an outerperipheral surface on part of which an outward flange is formed, theoutward flange having an axial side surface to which the second axialend surface of the first inner race is abutted for use, wherein theaxial length of the inner peripheral surface of the second inner race islarger than the axial length of the inner peripheral surface of thefirst inner race.